State Street Institutional Investment Trust · State Street Institutional Investment Trust STATE STREET INSTITUTIONAL LIQUID RESERVES FUND ... commercial paper and other high quality

State Street Institutional Investment Trust

STATE STREET INSTITUTIONAL LIQUID RESERVES FUND (SSIXX)STATE STREET INSTITUTIONAL TAX FREE MONEY MARKET FUND (SSTXX)

STATE STREET INSTITUTIONAL U.S. GOVERNMENT MONEY MARKET FUND (GVMXX)STATE STREET INSTITUTIONAL TREASURY MONEY MARKET FUND (TRIXX)

STATE STREET INSTITUTIONAL TREASURY PLUS MONEY MARKET FUND (TPIXX)

INSTITUTIONAL CLASS

Prospectus Dated April 30, 2013

THE SECURITIES AND EXCHANGE COMMISSION HAS NOT APPROVED OR DISAPPROVEDTHESE SECURITIES OR PASSED UPON THE ADEQUACY OF THIS PROSPECTUS. ANY REPRESENTA-TION TO THE CONTRARY IS A CRIMINAL OFFENSE.

AN INVESTMENT IN ANY OF THE FUNDS OFFERED BY THIS PROSPECTUS IS NOT A BANKDEPOSIT AND IS NOT INSURED OR GUARANTEED BY THE FEDERAL DEPOSIT INSURANCECORPORATION OR ANY OTHER GOVERNMENT AGENCY. ALTHOUGH THE FUNDS SEEK TOPRESERVE THE VALUE OF YOUR INVESTMENT AT $1.00 PER SHARE, IT IS POSSIBLE TO LOSEMONEY BY INVESTING IN THE FUNDS.

EACH FUND OFFERS MULTIPLE CLASSES OF SHARES. THIS PROSPECTUS COVERS ONLY THEINSTITUTIONAL CLASS.

TABLE OF CONTENTS

Fund Summaries

State Street Institutional Liquid Reserves Fund 3

State Street Institutional Tax Free Money Market Fund 7

State Street Institutional U.S. Government Money Market Fund 11

State Street Institutional Treasury Money Market Fund 15

State Street Institutional Treasury Plus Money Market Fund 18

Other Information 21

Additional Information About Investment Objectives, Principal Strategies and Risks of Investing in theFunds and Portfolios 22

Additional Information About the Funds’ and Portfolios’ Non-Principal Investment Strategies and Risks 29

Portfolio Holdings Disclosure 29

Management and Organization 29

Shareholder Information 30

Payments to Financial Intermediaries 34

Dividends, Distributions and Tax Considerations 34

Financial Highlights 36

2

STATE STREET INSTITUTIONAL LIQUIDRESERVES FUND

Investment Objective

The investment objective of State Street Institu-tional Liquid Reserves Fund (the “ILR Fund” or some-times referred to in context as the “Fund”) is to seek tomaximize current income, to the extent consistent withthe preservation of capital and liquidity and the main-tenance of a stable $1.00 per share net asset value(“NAV”) by investing in U.S. dollar-denominatedmoney market securities.

Fees and Expenses of the Fund

The table below describes the fees and expensesthat you may pay if you buy and hold shares of the ILRFund. The expenses shown in the table and the Examplereflect the expenses of the Fund and the Fund’s propor-tionate share of the expenses of State Street MoneyMarket Portfolio (the “Money Market Portfolio” orsometimes referred to in context as the “Portfolio”).

Annual Fund Operating Expenses (expenses thatyou pay each year as a percentage of the value of yourinvestment)(1)

Management Fee 0.05%

Other Expenses 0.07%

Total Annual Fund OperatingExpenses(2) 0.12%

(1) Amounts reflect the total expenses of the MoneyMarket Portfolio and the Fund.

(2) The Fund’s investment adviser, SSgA FundsManagement, Inc. (the “Adviser” or “SSgA FM”),may voluntarily reduce all or a portion of its fees and/or reimburse expenses of the Fund to the extentnecessary to avoid negative yield (the “VoluntaryReduction”), or a yield below a specified level, whichmay vary from time to time in the Adviser’s solediscretion. The Fund has agreed, subject to certainlimitations, to reimburse the Adviser for the full dol-lar amount of any Voluntary Reduction incurred afterOctober 1, 2012. The Adviser may, in its sole dis-cretion, irrevocably waive receipt of any or allreimbursement amounts due from the Fund, withoutlimitation. Any future reimbursement by the Fund ofthe Voluntary Reduction would increase the Fund’sexpenses and reduce the Fund’s yield. There is noguarantee that the Voluntary Reduction will be ineffect at any given time or that the Fund will be ableto avoid a negative yield.

Example

This Example is intended to help you compare thecost of investing in the ILR Fund with the cost of inves-ting in other mutual funds.

The Example assumes that you invest $10,000 inthe Fund for the time periods indicated and then redeemall of your shares at the end of those periods. TheExample also assumes that your investment has a 5%return each year and that the Fund’s operating expensesremain the same. Although your actual costs may behigher or lower, based on these assumptions your costswould be:

1 Year 3 Years 5 Years 10 Years

$12 $39 $68 $154

Principal Investment Strategies

The ILR Fund invests substantially all of its invest-able assets in the Money Market Portfolio.

The Money Market Portfolio follows a disciplinedinvestment process in which the Portfolio’s investmentadviser, SSgA Funds Management, Inc. (the “Adviser”or “SSgA FM”), bases its decisions on the relativeattractiveness of different money market instruments. Inthe Adviser’s opinion, the attractiveness of an instru-ment may vary depending on the general level of inter-est rates, as well as imbalances of supply and demand inthe market. The Portfolio invests in accordance withregulatory requirements applicable to money marketfunds, which require, among other things, the Portfolioto invest only in short-term, high quality debt obliga-tions (generally, securities that have remaining matur-ities of 397 calendar days or less and either have beenrated in one of the two highest short-term rating catego-ries or are considered by the Portfolio to be of com-parable quality), to maintain a maximum dollar-weighted average maturity of 60 days or less, and tomeet requirements as to portfolio diversification andliquidity.

The Portfolio attempts to meet its investmentobjective by investing in a broad range of money marketinstruments. These may include among other things:U.S. government securities, including U.S. Treasurybills, notes and bonds and other securities issued orguaranteed as to principal or interest by the U.S.government or its agencies or instrumentalities; certifi-cates of deposits and time deposits of U.S. and foreignbanks; commercial paper and other high quality obliga-tions of U.S. or foreign companies; asset-backed secu-

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rities, including asset-backed commercial paper;mortgage-related securities; and repurchase agreements.These instruments may bear fixed, variable or floatingrates of interest or may be zero-coupon securities. ThePortfolio also may invest in shares of other moneymarket funds, including funds advised by the Adviser.Under normal market conditions, the Portfolio intendsto invest more than 25% of its total assets in bankobligations. A substantial portion of the Portfolio maybe invested in securities that are issued or traded pur-suant to exemptions from registration under the federalsecurities laws.

Principal Investment Risks

An investment in the Fund is not a deposit in abank and is not insured or guaranteed by the FederalDeposit Insurance Corporation or any other governmentagency. Although the Fund seeks to preserve the valueof your investment at $1.00 per share, it is possible tolose money by investing in the Fund.

In addition, the Fund is subject to the followingrisks:

• Risks of Investing Principally in Money MarketInstruments:

• Interest Rate Risk — The risk that interestrates will rise, causing the value of thePortfolio’s investments to fall. Also, therisk that as interest rates decline, theamount of income the Portfolio receives onits new investments generally will decline.

• Credit Risk — The risk that an issuer,guarantor or liquidity provider of aninstrument will be unable, or will be per-ceived to be unable, to make scheduledinterest or principal payments, and that thevalue of the instrument will fall as a result.

• Liquidity Risk — The risk that the Portfo-lio may not be able to sell some or all of itssecurities at desired prices, or may beunable to sell the securities at all, becauseof a lack of demand in the market for suchsecurities, or a liquidity provider defaultson its obligation to purchase the securitieswhen properly tendered by the Portfolio.

• Prepayment Risk and Extension Risk— Applicable primarily to mortgage-related and asset-backed securities, therisks that loan obligations may be repaid

faster or slower than expected, causing thePortfolio to invest repayment proceeds in,or continue to hold, lower yielding secu-rities, as the case may be.

• Stable Share Price Risk: If the market value ofone or more of the Portfolio’s investmentschanges substantially, the Fund may not be ableto maintain a stable share price of $1.00. Thisrisk typically is higher during periods of rapidlychanging interest rates or when issuer creditquality generally is falling, and is made worsewhen the Portfolio experiences significantredemption requests.

• Master/Feeder Structure Risk: The Fund’sperformance may be adversely affected as aresult of large cash inflows to or outflows fromthe Portfolio and any related disruption to thePortfolio’s investment program.

• Low Short-Term Interest Rate Risk: At thedate of this Prospectus, short-term interest ratesare at historically low levels, and so the Fund’syield is very low. It is possible that the Portfoliowill generate an insufficient amount of incometo pay its expenses, and that it and/or the Fundwill not be able to pay a daily dividend and mayhave a negative yield (i.e., it may lose money onan operating basis). It is possible that the Portfo-lio will maintain a substantial portion of itsassets in cash, on which it would earn little, ifany, income.

• Banking Industry Risk: To the extent the Port-folio concentrates its investments in bankobligations, financial, economic, business, andother developments in the banking industry willhave a greater effect on the Portfolio than if ithad not concentrated its assets in the bankingindustry. Adverse changes in the bankingindustry may include, among other things, banksexperiencing substantial losses on loans,increases in non-performing assets and charge-offs and declines in total deposits.

• Repurchase Agreement Risk: In a repurchaseagreement, the Portfolio purchases a securityfrom a seller at one price and simultaneouslyagrees to sell it back to the original seller at anagreed-upon price. If the Portfolio’s counter-party is unable to honor its commitments, thePortfolio may be unable to recover its purchaseprice and may be prevented or delayed fromrealizing on the security to make up any losses.

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• Mortgage-Related and Asset-Backed SecuritiesRisk: Defaults, or perceived increases in the riskof defaults, on the loans underlying mortgage-related or asset-backed securities may impair thevalues of the securities. These securities alsopresent a higher degree of prepayment risk (whenrepayment of principal occurs before scheduledmaturity) and extension risk (when rates ofrepayment of principal are slower than expected)than do other types of fixed income securities.The enforceability of security interests that sup-port these securities may, in some cases, be sub-ject to limitations.

• Foreign Securities Risk: The Portfolio mayinvest in U.S. dollar denominated instrumentsissued by foreign governments, corporations andfinancial institutions. Foreign securities are sub-ject to political, economic, and regulatory risksnot present in domestic investments. Returns oninvestments in securities issued by foreignissuers could be more volatile than securitiesissued by U.S. issuers. Foreign investments maybe affected by, among other things, changes incurrency exchange rates; currency controls; dif-ferent accounting, auditing, financial reporting,and legal standards and practices applicable inforeign countries; tax withholding; and highertransaction costs. Foreign banks, or their domes-tic or foreign branches, may be subject to lessrigorous regulation than U.S. banks operating inthe United States, and may not be required tomeet financial, capital, and other requirementsapplicable to U.S. banks. Foreign laws andaccounting standards typically are not as strict asthey are in the U.S. so there may be fewerrestrictions on loan limitations, less frequentexaminations and less stringent requirementsregarding reserve accounting, auditing, record-keeping and public reporting requirements.

• U.S. Government Securities Risk: Securitiesof certain U.S. government agencies andinstrumentalities are not supported by the fullfaith and credit of the U.S. Government, and tothe extent the Portfolio owns such securities, itmust look to the agency or instrumentality issu-ing or guaranteeing the securities for repayment.

• Variable and Floating Rate Securities Risk:The Portfolio may purchase variable and float-ing rate securities, whose interest rates changebased on changes in market interest rates. As aresult, the interest paid on such securities will

tend to fall as market interest rates fall generally,and the interest rates on such securities may notrise as rapidly as general market rates.

• Market Risk: The values of the securities inwhich the Portfolio invests may go up or downin response to the prospects of individual issuersand/or general economic conditions. Pricechanges may be temporary or may last forextended periods. Recent instability in thefinancial markets has led the U.S. Governmentto take a number of unprecedented actionsdesigned to support certain financial institutionsand segments of the financial markets that haveexperienced extreme volatility and, in somecases, a lack of liquidity. The withdrawal of thissupport could negatively affect the value andliquidity of certain securities or of markets gen-erally. In addition, legislation recently enacted inthe U.S. calls for changes in many aspects offinancial regulation. The impact of the legis-lation on the markets, and the practicalimplications for market participants, may not befully known for some time.

• Money Market Fund Regulatory Risk: It ispossible that the Securities and ExchangeCommission (“SEC”) or another agency willadopt regulations that change in very importantrespects the operation of money market funds.Any such regulatory changes could impactimportant characteristics of the Fund, includingliquidity of an investment in the Fund or theFund’s ability to maintain a stable net assetvalue per share.

Performance

The bar chart and table below provide someindication of the risks of investing in the ILR Fund byillustrating the variability of the Fund’s returns duringthe years since inception. The Fund’s past performancedoes not necessarily indicate how the Fund will performin the future. Current performance information for theFund is available toll free by calling (877) 521-4083 orby visiting our website at www.ssga.com/cash.

5

State Street Institutional Liquid Reserves FundTotal Return for the Calendar Years

Ended December 31

5.28%

2.82%

0.19% 0.15% 0.20%0.49%

5.07%

3.19%

0%

3%

6%2005 2006 2007 2008 2009 2010 20122011

Returns would have been lower if operatingexpenses had not been reduced. During the periodshown in the bar chart, the highest return for a quarterwas 1.33% (quarter ended 12/31/06) and the lowestreturn for a quarter was 0.03% (quarter ended 9/30/11).

Average Annual Total ReturnsFor the Periods Ended December 31, 2012

1-Year 5-YearSince the InceptionDate of the Fund

State Street InstitutionalLiquid ReservesFund . . . . . . . . . . . . . . 0.20% 0.77% 2.13%

To obtain the Fund’s current yield, please call(877) 521-4083.

Investment Adviser

SSgA FM serves as the investment adviser to theFund.

Purchase and Sale of Fund Shares

For important information about purchase and saleof Fund shares, please turn to “Other Information” onpage 21 of the prospectus.

Tax Information

The Fund intends to make distributions that may betaxed as ordinary income or capital gains.

Payments to Broker-Dealers and Other FinancialIntermediaries

For important information about financial interme-diary compensation, please turn to “Other Information”on page 21 of the prospectus.

6

STATE STREET INSTITUTIONAL TAX FREEMONEY MARKET FUND


The investment objective of State Street Institu-tional Tax Free Money Market Fund (the “Tax FreeFund” or sometimes referred to in context as the“Fund”) is to seek to maximize current income, exemptfrom federal income taxes, to the extent consistent withthe preservation of capital and liquidity and the main-tenance of a stable $1.00 per share net asset value(“NAV”).


The table below describes the fees and expensesthat you may pay if you buy and hold shares of the TaxFree Fund. The expenses shown in the table and theExample reflect the expenses of the Fund and theFund’s proportionate share of the expenses of StateStreet Tax Free Money Market Portfolio (the “Tax FreePortfolio” or sometimes referred to in context as the“Portfolio”).





(1) Amounts reflect the total expenses of the Tax FreePortfolio and the Fund.

(2) The Fund’s investment adviser, SSgA Funds Man-agement, Inc. (the “Adviser” or “SSgA FM”), mayvoluntarily reduce all or a portion of its fees and/orreimburse expenses of the Fund to the extent neces-sary to avoid negative yield (the “VoluntaryReduction”), or a yield below a specified level,which may vary from time to time in the Adviser’ssole discretion. The Fund has agreed, subject tocertain limitations, to reimburse the Adviser for thefull dollar amount of any Voluntary Reductionincurred after October 1, 2012. The Adviser may, inits sole discretion, irrevocably waive receipt of anyor all reimbursement amounts due from the Fund,without limitation. Any future reimbursement by theFund of the Voluntary Reduction would increase theFund’s expenses and reduce the Fund’s yield. Thereis no guarantee that the Voluntary Reduction will bein effect at any given time or that the Fund will beable to avoid a negative yield.

Example

This Example is intended to help you compare thecost of investing in the Tax Free Fund with the costs ofinvesting in other mutual funds.

The Example assumes that you invest $10,000 inthe Fund for the time periods indicated and then redeemall of your shares at the end of those periods. TheExample also assumes that your investment has a 5%return each year and that the Fund’s operating expensesremain the same. Although your actual costs may behigher or lower, based on these assumptions yours costswould be:


$20 $64 $113 $255


The Tax Free Fund invests substantially all of itsinvestable assets in the Tax Free Portfolio.

The Tax Free Portfolio has a fundamental policy ofinvesting at least 80% of its net assets (plus borrowings,if any) in federal tax-exempt, high quality, short-termmunicipal securities of all types. The Portfolio generallyinvests substantially all of its assets in instrumentsexempt from ordinary federal income tax. However, thePortfolio may invest up to 20% of its net assets infederally taxable money market instruments (includingthose subject to the Federal alternative minimum tax),including securities issued by or guaranteed as toprincipal or interest by the U.S. government or its agen-cies and instrumentalities, as well as certificates ofdeposit, commercial paper and repurchase agreements.The Portfolio may buy or sell securities on a when-issued or forward commitment basis.

The Portfolio follows a disciplined investmentprocess that attempts to provide stability of principal,liquidity and current income through all market con-ditions, by investing in high quality money marketinstruments. Among other things, the Portfolio’sinvestment adviser, SSgA Funds Management, Inc. (the“Adviser” or “SSgA FM”), conducts its own creditanalyses of potential investments and portfolio holdings,and relies substantially on a dedicated short-term creditresearch team. The Portfolio invests in accordance withregulatory requirements applicable to money marketfunds, which require, among other things, the Portfolioto invest only in short-term, high quality debt obliga-tions (generally, securities that have remaining matur-ities of 397 calendar days or less and either have been

7

rated in one of the two highest short-term rating catego-ries or are considered by the Portfolio to be of com-parable quality), to maintain a maximum dollar-weighted average maturity of 60 days or less, and tomeet requirements as to portfolio diversification andliquidity. All securities held by the Portfolio are U.S.dollar-denominated, and they may have fixed, variableor floating interest rates, or may be zero-couponsecurities.

The Portfolio attempts to meet its investmentobjective by investing in, among other things:

• Securities issued by states, municipalities andtheir political subdivisions and agencies andcertain territories and possessions of the U.S.(“municipal securities”), including:

• General obligation bonds and notes;

• Revenue bonds and notes;

• Commercial paper and other privatelyissued securities;

• Tender option bonds;

• Private activity bonds;

• Industrial development bonds;

• Municipal lease contracts; and

• Securities of other investment companieswith similar investment guidelines.


An investment in the Fund is not a deposit in abank and it is not insured or guaranteed by the FederalDeposit Insurance Corporation or any other governmentagency. Although the Fund seeks to preserve the valueof your investment at $1.00 per share, it is possible tolose money by investing in the Fund.









• Municipal Securities Risk: The municipalsecurities markets in which the Portfolio investsmay be volatile and may be significantlyaffected by adverse tax, legislative, or politicalchanges and the financial condition of theissuers of municipal securities. The values ofmunicipal securities that depend on a specificrevenue source to fund their payment obligationsmay fluctuate as a result of changes in the cashflows generated by the revenue source orchanges in the priority of the municipal securityto receive the cash flows generated by the rev-enue source.

8


• Market Risk: The values of the securities inwhich the Portfolio invests may go up or downin response to the prospects of individual issuersand/or general economic conditions. Pricechanges may be temporary or may last forextended periods. Recent instability in thefinancial markets has led the U.S. Governmentto take a number of unprecedented actionsdesigned to support certain financial institutionsand segments of the financial markets that haveexperienced extreme volatility and, in somecases, a lack of liquidity. The withdrawal of thissupport could negatively affect the value andliquidity of certain securities or of markets gen-erally. In addition, legislation recently enacted inthe U.S. calls for changes in many aspects offinancial regulation. The impact of the legis-lation on the markets and the practicalimplications for market participants, may not befully known for some time.

• Variable and Floating Rate Securities Risk: ThePortfolio may purchase variable and floating ratesecurities, whose interest rates change based onchanges in market interest rates. As a result, theinterest paid on such securities will tend to fall asmarket interest rates fall generally, and the interestrates on such securities may not rise as rapidly asgeneral market rates.


Performance

The bar chart and table below provide someindication of the risks of investing in the Tax Free Fundby illustrating the variability of the Fund’s returns duringthe years since inception. The Fund’s past performancedoes not necessarily indicate how the Fund will performin the future. Current performance information for theFund is available toll free by calling (877) 521-4083 or byvisiting our website at www.ssga.com/cash.

State Street Institutional Tax FreeMoney Market Fund

Total Return for the Calendar YearsEnded December 31

0.43%

0.10% 0.02% 0.00%

2.31%

2011 2012201020092008

0%

2%

4%

During the period shown in the bar chart, the high-est return for a quarter was 0.70% (quarter ended3/31/08) and the lowest return for a quarter was 0.00%(quarter ended 12/31/12).



State Street InstitutionalTax Free MoneyMarket Fund . . . . . . . . 0.00% 0.57% 1.01%


Investment Adviser




9

Tax Information

The Fund intends to distribute income that isexempt from U.S. federal income tax and theU.S. federal alternative minimum tax. However, aportion of the Fund’s distributions may be subject tofederal income tax or to federal alternative minimumtax.



10

STATE STREET INSTITUTIONAL U.S.GOVERNMENT MONEY MARKET FUND


The investment objective of State Street Institu-tional U.S. Government Money Market Fund (the “U.S.Government Fund” or sometimes referred to in contextas the “Fund”) is to seek to maximize current income, tothe extent consistent with the preservation of capital andliquidity and the maintenance of a stable $1.00 per sharenet asset value (“NAV”).


The table below describes the fees and expensesthat you may pay if you buy and hold shares of the U.S.Government Fund. The expenses shown in the table andthe Example reflect the expenses of the Fund and theFund’s proportionate share of the expenses of StateStreet U.S. Government Money Market Portfolio (the“U.S. Government Portfolio” or sometimes referred toin context as the “Portfolio”).




Total Annual Fund OperatingExpenses 0.13%

Fee Waiver and/or ExpenseReimbursement(2) (0.01)%

Total Annual Fund OperatingExpense After Fee Waiver and/or Expense Reimbursement(3) 0.12%

(1) Amounts reflect the total expenses of the U.S. Gov-ernment Portfolio and the Fund.

(2) The U.S. Government Fund’s investment adviser,SSgA Funds Management, Inc. (the “Adviser” or“SSgA FM”), has contractually agreed to cap theFund’s Total Annual Fund Operating Expenses(excluding taxes, interest and extraordinaryexpenses) attributable to the Institutional Class tothe extent that expenses exceed 0.12% of Institu-tional Class net assets, through April 30, 2014; thesearrangements may not be terminated prior to thatdate without the consent of the Board.

(3) The Adviser may also voluntarily reduce all or aportion of its fees and/or reimburse expenses of theFund to the extent necessary to avoid negative yield

(the “Voluntary Reduction”), or a yield below aspecified level, which may vary from time to time inthe Adviser’s sole discretion. The Fund has agreed,subject to certain limitations, to reimburse theAdviser for the full dollar amount of any VoluntaryReduction incurred after October 1, 2012. TheAdviser may, in its sole discretion, irrevocablywaive receipt of any or all reimbursement amountsdue from the Fund, without limitation. Any futurereimbursement by the Fund of the Voluntary Reduc-tion would increase the Fund’s expenses and reducethe Fund’s yield. There is no guarantee that theVoluntary Reduction will be in effect at any giventime or that the Fund will be able to avoid a negativeyield.

Example

This Example is intended to help you compare thecost of investing in the U.S. Government Fund with thecost of investing in other mutual funds.

The Example assumes that you invest $10,000 inthe Fund for the time periods indicated and thenredeem all of your shares at the end of those periods.The Example also assumes that your investment has a5% return each year and that the Fund’s operatingexpenses remain the same. Although your actual costsmay be higher or lower, based on these assumptionsyour costs would be:


$12 $41 $72 $165


The U.S. Government Fund invests substantiallyall of its investable assets in the U.S. GovernmentPortfolio.

The U.S. Government Portfolio typically invests atleast 80% of its net assets (plus borrowings, if any) inobligations issued or guaranteed as to principal or inter-est by the U.S. government or its agencies andinstrumentalities, as well as repurchase agreementssecured by such instruments.

The Portfolio follows a disciplined investmentprocess that attempts to provide stability of principal,liquidity and current income, by investing in U.S. gov-ernment securities and other high quality money marketinstruments. Among other things, SSgA FM, the Portfo-lio’s investment adviser, conducts its own credit analy-ses of potential investments and portfolio holdings, and

11

relies substantially on a dedicated short-term creditresearch team. The Portfolio invests in accordance withregulatory requirements applicable to money marketfunds, which require, among other things, the Portfolioto invest only in short-term, high quality debt obliga-tions (generally, securities that have remaining matur-ities of 397 calendar days or less and either have beenrated in one of the two highest short-term rating catego-ries or are considered by the Portfolio to be of com-parable quality), to maintain a maximum dollar-weighted average maturity of 60 days or less, and tomeet requirements as to portfolio diversification andliquidity. All securities held by the Portfolio are U.S.dollar-denominated, and they may have fixed, variableor floating interest rates.


• Obligations issued or guaranteed as to principal orinterest by the U.S. government or its agencies andinstrumentalities, such as U.S. Treasury securitiesand securities issued by the Government NationalMortgage Association (“GNMA”), which arebacked by the full faith and credit of the UnitedStates;

• Obligations issued or guaranteed by the FederalHome Loan Mortgage Corporation, the FederalNational Mortgage Association, and U.S.government-sponsored entities such as the FederalHome Loan Bank, which are not backed by the fullfaith and credit of the United States; and

• Repurchase agreements with respect to U.S.government securities





• Interest Rate Risk — The risk that interestrates will rise, causing the value of thePortfolio’s investments to fall. Also, therisk that as interest rates decline, the

amount of income the Portfolio receives onits new investments generally will decline.



• Prepayment Risk and Extension Risk —Applicable primarily to mortgage-relatedand asset-backed securities, the risks thatloan obligations may be repaid faster orslower than expected, causing the Portfolioto invest repayment proceeds in, or con-tinue to hold, lower yielding securities, asthe case may be.


• U.S. Government Securities Risk: Securities ofcertain U.S. government agencies andinstrumentalities are not supported by the fullfaith and credit of the U.S. Government, and tothe extent the Portfolio owns such securities, itmust look to the agency or instrumentality issu-ing or guaranteeing the securities for repayment.Because the Portfolio emphasizes investment inU.S. government securities, and because U.S.government securities generally are perceived ashaving low risks compared to most other typesof investments, the Portfolio’s performancecompared to money market funds that investprincipally in other types of money marketinstruments may be lower.

• Significant Exposure to U.S. Government Agen-cies Risk: To the extent the Portfolio focusesits investments in securities issued or guaranteedby U.S. government agencies, any market pricemovements, regulatory changes or changes inpolitical or economic conditions that affect the

12

U.S. government agencies in which the Portfolioinvests may have a significant impact on thePortfolio’s performance. Events that wouldadversely affect the market prices of securitiesissued or guaranteed by one government agencymay adversely affect the market price of secu-rities issued or guaranteed by other governmentagencies.

• Mortgage-Related and Asset-Backed SecuritiesRisk: Defaults, or perceived increases in the riskof defaults, on the loans underlying mortgage-related or asset-backed securities may impair thevalues of the securities. These securities alsopresent a higher degree of prepayment risk (whenrepayment of principal occurs before scheduledmaturity) and extension risk (when rates ofrepayment of principal are slower than expected)than do other types of fixed income securities.




• Market Risk: The values of the securities inwhich the Portfolio invests may go up or downin response to the prospects of individual issuersand general economic conditions. Price changesmay be temporary or may last for extendedperiods. Recent instability in the financial mar-kets has led the U.S. Government to take anumber of unprecedented actions designed tosupport certain financial institutions and seg-ments of the financial markets that have experi-enced extreme volatility and, in some cases, alack of liquidity. The withdrawal of this supportcould negatively affect the value and liquidity ofcertain securities or of markets generally. Inaddition, legislation recently enacted in the U.S.calls for changes in many aspects of financialregulation. The impact of the legislation on themarkets, and the practical implications for mar-ket participants, may not be fully known forsome time.

• Variable and Floating Rate Securities Risk: ThePortfolio may purchase variable and floating ratesecurities, whose interest rates change based onchanges in market interest rates. As a result, theinterest paid on such securities will tend to fall asmarket interest rates fall generally, and the interestrates on such securities may not rise as rapidly asgeneral market rates.


Performance

The bar chart and table below provide someindication of the risks of investing in the U.S. GovernmentFund by illustrating the variability of the Fund’s returnsduring the years since inception. The Fund’s past perform-ance does not necessarily indicate how the Fund will per-form in the future. Current performance information for theFund is available toll free by calling (877) 521-4083 or byvisiting our website at www.ssga.com/cash.

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State Street Institutional U.S. GovernmentMoney Market Fund


0.26%0.07% 0.02% 0.03%

2.17%

2011 2012201020092008

0%

2%

4%




State Street InstitutionalU.S. GovernmentMoney MarketFund . . . . . . . . . . . . . . 0.03% 0.51% 0.65%


Investment Adviser




Tax Information




14

STATE STREET INSTITUTIONAL TREASURYMONEY MARKET FUND


The investment objective of State Street Institu-tional Treasury Money Market Fund (the “TreasuryFund” or sometimes referred to in context as the“Fund”) is to seek a high level of current income con-sistent with preserving principal and liquidity and themaintenance of a stable $1.00 per share net asset value(“NAV”).


The table below describes the fees and expensesthat you may pay if you buy and hold shares of theTreasury Fund. The expenses shown in the table and theExample reflect the expenses of the Fund and theFund’s proportionate share of the expenses of StateStreet Treasury Money Market Portfolio (the “TreasuryPortfolio” or sometimes referred to in context as the“Portfolio”).





(1) Amounts reflect the total expenses of the TreasuryPortfolio and the Fund.

(2) The Fund’s investment adviser, SSgA Funds Man-agement, Inc. (the “Adviser” or “SSgA FM”), mayvoluntarily reduce all or a portion of its fees and/orreimburse expenses of the Fund to the extent neces-sary to avoid negative yield (the “VoluntaryReduction”), or a yield below a specified level,which may vary from time to time in the Adviser’ssole discretion. The Fund has agreed, subject tocertain limitations, to reimburse the Adviser for thefull dollar amount of any Voluntary Reductionincurred after October 1, 2012. The Adviser may, inits sole discretion, irrevocably waive receipt of anyor all reimbursement amounts due from the Fund,without limitation. Any future reimbursement by theFund of the Voluntary Reduction would increase theFund’s expenses and reduce the Fund’s yield. Thereis no guarantee that the Voluntary Reduction will bein effect at any given time or that the Fund will beable to avoid a negative yield.

Example

This Example is intended to help you compare thecost of investing in the Treasury Fund with the cost ofinvesting in other mutual funds.

The Example assumes that you invest $10,000 inthe Fund for the time periods indicated and then redeemall of your shares at the end of those periods. TheExample also assumes that your investment has a 5%return each year and that the Fund’s operating expensesremain the same. Although your actual costs may behigher or lower, based on these assumptions your costswould be:


$12 $39 $68 $154


The Treasury Fund invests substantially all of itsinvestable assets in the Treasury Portfolio.

The Treasury Portfolio attempts to meet its invest-ment objective by investing at least 80% of its net assetsin U.S. Treasury bills, notes and bonds (which are directobligations of the U.S. government). Under normalconditions, the Portfolio will invest substantially all ofits assets in such securities. The Portfolio also mayinvest in shares of other money market funds, includingfunds advised by the Portfolio’s investment adviser,SSgA Funds Management, Inc. (the “Adviser” or“SSgA FM”).

The Portfolio invests in accordance with regulatoryrequirements applicable to money market funds, whichrequire, among other things, the Portfolio to invest onlyin short-term securities (generally, securities that haveremaining maturities of 397 calendar days or less), tomaintain a maximum dollar-weighted average maturityof 60 days or less, and to meet requirements as toportfolio diversification and liquidity.



15






• Stable Share Price Risk: If the market value ofone or more of the Portfolio’s investmentschanges substantially, the Fund may not be ableto maintain a stable share price of $1.00. Thisrisk typically is higher during periods of rapidlychanging interest rates or when issuer creditquality generally is falling and is made worsewhen the Portfolio experiences significantredemption requests.


• Market Risk: Recent instability in the financialmarkets has led the U.S. Government to take anumber of unprecedented actions designed tosupport certain financial institutions and seg-ments of the financial markets that haveexperienced extreme volatility and, in some

cases, a lack of liquidity. The withdrawal of thissupport could negatively affect the value andliquidity of certain securities or of markets gen-erally. In addition, legislation recently enacted inthe U.S. calls for changes in many aspects offinancial regulation. The impact of the legis-lation on the markets, and the practicalimplications for market participants, may not befully known for some time.


Performance

The bar chart and table below provide someindication of the risks of investing in the Treasury Fundby illustrating the variability of the Fund’s returns duringthe years since inception. The Fund’s past performancedoes not necessarily indicate how the Fund will performin the future. Current performance information for theFund is available toll free by calling (877) 521-4083 or byvisiting our website at www.ssga.com/cash.

State Street Institutional Treasury MoneyMarket Fund


0.04% 0.01% 0.01% 0.00%

1.24%

2011 2012201020092008

0%

1%

2%

During the period shown in the bar chart, the high-est return for a quarter was 0.53% (quarter ended3/31/08) and the lowest return for a quarter was 0.00%(quarter ended 9/30/12).

16



State Street InstitutionalTreasury MoneyMarket Fund . . . . . . . . 0.00% 0.26% 0.36%


Investment Adviser




Tax Information




17

STATE STREET INSTITUTIONAL TREASURYPLUS MONEY MARKET FUND


The investment objective of State Street Institu-tional Treasury Plus Money Market Fund (the “TreasuryPlus Fund” or sometimes referred to in context as the“Fund”) is to seek a high level of current income con-sistent with preserving principal and liquidity and themaintenance of a stable $1.00 per share net asset value(“NAV”).


The table below describes the fees and expensesthat you may pay if you buy and hold shares of theTreasury Plus Fund. The expenses shown in the tableand the Example reflect the expenses of the Fund andthe Fund’s proportionate share of the expenses of StateStreet Treasury Plus Money Market Portfolio (the“Treasury Plus Portfolio” or sometimes referred to inthis context as the “Portfolio”).




Total Annual Fund OperatingExpenses 0.14%

Fee Waiver and/or ExpenseReimbursement(2) (0.02)%

Total Annual Fund OperatingExpenses After Fee Waiver and/or Expense Reimbursement(3) 0.12%

(1) Amounts reflect the total expenses of the TreasuryPlus Portfolio and the Fund restated to reflect cur-rent fees.

(2) The Treasury Plus Fund’s investment adviser, SSgAFunds Management, Inc. (the “Adviser” or “SSgAFM”) has contractually agreed to cap the Fund’sTotal Annual Fund Operating Expenses (excludingtaxes, interest and extraordinary expenses) attribut-able to the Institutional Class to the extent thatexpenses exceed 0.12% of Institutional Class netassets, through April 30, 2014; these arrangementsmay not be terminated prior to that date without theconsent of the Board.

(3) The Adviser may also voluntarily reduce all or aportion of its fees and/or reimburse expenses of theFund to the extent necessary to avoid negative yield(the “Voluntary Reduction”), or a yield below aspecified level, which may vary from time to time inthe Adviser’s sole discretion. The Fund has agreed,subject to certain limitations, to reimburse theAdviser for the full dollar amount of any VoluntaryReduction incurred after October 1, 2012. TheAdviser may, in its sole discretion, irrevocablywaive receipt of any or all reimbursement amountsdue from the Fund, without limitation. Any futurereimbursement by the Fund of the Voluntary Reduc-tion would increase the Fund’s expenses and reducethe Fund’s yield. There is no guarantee that theVoluntary Reduction will be in effect at any giventime or that the Fund will be able to avoid a negativeyield.

Example

This Example is intended to help you compare thecost of investing in the Treasury Plus Fund with the costof investing in other mutual funds.

The Example assumes that you invest $10,000 inthe Fund for the time periods indicated and then redeemall of your shares at the end of those periods. TheExample also assumes that your investment has a 5%return each year, that the Fund’s operating expensesremain the same, and that that the “1 Year” figurereflects the impact of fee waivers and/or expensereimbursements for the first year, as shown in the“Annual Fund Operating Expenses” table. Althoughyour actual costs may be higher or lower, based on theseassumptions your costs would be:


$12 $43 $77 $177


The Treasury Plus Fund invests substantially all ofits investable assets in the Treasury Plus Portfolio.

The Treasury Plus Portfolio attempts to meet itsinvestment objective by investing, under normalcircumstances, at least 80% of its net assets in U.S.Treasury bills, notes and bonds (which are direct obliga-tions of the U.S. government) and repurchase agree-ments collateralized by these obligations. The Portfolioalso may invest in shares of other money market funds,including funds advised by the Adviser.

18










• Stable Share Price Risk: If the market value ofone or more of the Portfolio’s investmentschanges substantially during the period, the

Fund may not be able to maintain a stable shareprice of $1.00. This risk typically is higher dur-ing periods of rapidly changing interest rates orwhen issuer credit quality generally is falling,and is made worse when the Portfolio experi-ences significant redemption requests.

• Low Short-Term Interest Rate Risk: At the dateof this Prospectus, short-term interest rates are athistorically low levels, and so the Fund’s yield isvery low. It is possible that the Portfolio willgenerate an insufficient amount of income to payits expenses, and that it and/or the Fund will notbe able to pay a daily dividend and may have anegative yield (i.e., it may lose money on anoperating basis). It is possible that the Portfoliowill maintain a substantial portion of its assets incash, on which it would earn little, if any, income.


• Market Risk: Recent instability in the financialmarkets has led the U.S. Government to take anumber of unprecedented actions designed tosupport certain financial institutions and seg-ments of the financial markets that have experi-enced extreme volatility and, in some cases, alack of liquidity. The withdrawal of this supportcould negatively affect the value and liquidity ofcertain securities or of markets generally. Inaddition, legislation recently enacted in the U.S.calls for changes in many aspects of financialregulation. The impact of the legislation on themarkets, and the practical implications for mar-ket participants, may not be fully known forsome time.


19

• U.S. Government Securities Risk: Securities ofcertain U.S. government agencies and instru-mentalities are not supported by the full faithand credit of the U.S. Government, and to theextent the Portfolio owns such securities, it mustlook to the agency or instrumentality issuing orguaranteeing the securities for repayment.

Performance

The bar chart and table below provide someindication of the risks of investing in the Treasury PlusFund by illustrating the variability of the Fund’s returnsduring the years since inception. The Fund’s past perform-ance does not necessarily indicate how the Fund will per-form in the future. Current performance information for theFund is available toll free by calling (877) 521-4083 or byvisiting our website at www.ssga.com/cash.

State Street Institutional Treasury PlusMoney Market Fund


0.06% 0.04% 0.01% 0.02%

1.55%

2011 2012201020092008

0%

1%

2%




State Street InstitutionalTreasury Plus MoneyMarket Fund . . . . . . . . 0.02% 0.33% 0.46%


Investment Adviser




Tax Information




20

OTHER INFORMATION


Purchase Minimums

To establish an account $25,000,000

To add to an existing account No minimum

You may redeem Fund shares on any day the Fundis open for business.

You may redeem Fund shares by written request orwire transfer. Written requests should be sent to:

By Mail:State Street Institutional Trust FundsP.O. Box 8048Boston, MA 02266-8048

By Overnight:State Street Institutional Trust Funds30 Dan RoadCanton, MA 02021-2809

By Telephone:For wire transfer instructions, please call (866) 392-0869

between 8 a.m. and 5 p.m. Eastern time. Redemptions by tele-phone are permitted only if you previously have been authorizedfor these transactions.

If you wish to purchase or redeem Fund shares through abroker, bank or other financial intermediary, please contact thatfinancial intermediary directly. Your financial intermediary mayhave different or additional requirements for opening an accountand/or for the processing of purchase and redemption orders, ormay be closed at times when the Fund is open.

Payments to Brokers and Other FinancialIntermediaries

If you purchase the Fund through a broker or otherfinancial intermediary (such as a bank), the Fund and itsaffiliates may pay the intermediary for the sale of Fundshares and related services. These payments may createa conflict of interest by influencing the broker or otherintermediary and your salesperson to recommend theFund over another investment. Ask your salesperson orvisit your financial intermediary’s Website for moreinformation.

21

ADDITIONAL INFORMATION ABOUTINVESTMENT OBJECTIVES, PRINCIPALSTRATEGIES AND RISKS OF INVESTING INTHE FUNDS AND PORTFOLIOS

Investment Objectives

The investment objective of each of the ILR Fund,the U.S. Government Fund, the Treasury Fund and theTreasury Plus Fund, as stated in each Fund’s FundSummary, may be changed without shareholder appro-val. The Investment objective of the Tax Free Fund, asstated in the Fund’s Fund Summary, is fundamental andmay not be changed without shareholder approval.

ILR FUND


The ILR Fund invests substantially all of its invest-able assets in the Money Market Portfolio.

The Money Market Portfolio follows a disciplinedinvestment process in which the Adviser bases its deci-sions on the relative attractiveness of different moneymarket instruments. In the Adviser’s opinion, the attrac-tiveness of an instrument may vary depending on thegeneral level of interest rates, as well as imbalances ofsupply and demand in the market. The Portfolio investsin accordance with regulatory requirements applicableto money market funds, which require, among otherthings, the Portfolio to invest only in short-term, highquality debt obligations (generally, securities that haveremaining maturities of 397 calendar days or less andeither have been rated in one of the two highest short-term rating categories or are considered by the Portfolioto be of comparable quality), to maintain a maximumdollar-weighted average maturity of 60 days or less, andto meet requirements as to portfolio diversification andliquidity.

The Portfolio attempts to meet its investmentobjective by investing in a broad range of money marketinstruments. These may include among other things:U.S. government securities, including U.S. Treasurybills, notes and bonds and other securities issued orguaranteed as to principal or interest by the U.S.government or its agencies or instrumentalities; certifi-cates of deposits and time deposits of U.S. and foreignbanks (including ECDs, ETDs and YCDs (as definedbelow)); commercial paper and other high qualityobligations of U.S. or foreign companies; asset-backedsecurities, including asset-backed commercial paper;mortgage-related securities; and repurchase agreements.

These instruments may bear fixed, variable or floatingrates of interest or may be zero-coupon securities. ThePortfolio also may invest in shares of other moneymarket funds, including funds advised by the Adviser.Under normal market conditions, the Portfolio intendsto invest more than 25% of its total assets in bankobligations. A substantial portion of the Portfolio maybe invested in securities that are issued or tradedpursuant to exemptions from registration under thefederal securities laws. European Certificates of Deposit(“ECDs”) are U.S. dollar-denominated certificates ofdeposit issued by a bank outside of the United States.European Time Deposits (“ETDs”) are U.S. dollar-denominated deposits in foreign branches of U.S. banksand foreign banks. Yankee Certificates of Deposit(“YCDs”) are U.S. dollar-denominated certificates ofdeposit issued by U.S. branches of foreign banks. Theseinstruments have different risks than those associatedwith the obligations of U.S. banks operating in theUnited States.

TAX FREE FUND


The Tax Free Fund invests substantially all of itsinvestable assets in the Tax Free Portfolio.

The Tax Free Portfolio has a fundamental policy ofinvesting at least 80% of its net assets (plus borrowings,if any) in federal tax-exempt, high quality, short-termmunicipal securities of all types. The Portfolio generallyinvests all of its assets in instruments exempt fromordinary federal income tax. The Portfolio may investup to 20% of its net assets in federally taxable moneymarket instruments (including those subject to theFederal alternative minimum tax), including securitiesissued by or guaranteed as to principal or interest by theU.S. government or its agencies and instrumentalities, aswell as certificates of deposit, commercial paper andrepurchase agreements. The Portfolio may buy or sellsecurities on a when-issued or forward commitmentbasis.

The Portfolio follows a disciplined investmentprocess that attempts to provide stability of principal,liquidity and current income through all market con-ditions, by investing in high quality money marketinstruments. Among other things, the Adviser conductsits own credit analyses of potential investments andportfolio holdings, and relies substantially on a dedi-cated short-term credit research team. The Portfolio

22

invests in accordance with regulatory requirementsapplicable to money market funds, which require,among other things, the Portfolio to invest only in short-term, high quality debt obligations (generally, securitiesthat have remaining maturities of 397 calendar days orless and either have been rated in one of the two highestshort-term rating categories or are considered by thePortfolio to be of comparable quality), to maintain amaximum dollarweighted average maturity of 60 daysor less, and to meet requirements as to portfoliodiversification and liquidity. All securities held by thePortfolio are U.S. dollar-denominated, and they mayhave fixed, variable or floating interest rates, or may bezero-coupon securities.


• Municipal securities, including:

• General obligation bonds and notes;

• Revenue bonds and notes;

• Commercial paper and other privatelyissued securities;

• Tender option bonds;

• Private activity bonds;

• Industrial development bonds;

• Municipal lease contracts; and

• Securities of other investment companieswith similar investment guidelines.

U.S. GOVERNMENT FUND


The U.S. Government Fund invests substantiallyall of its investable assets in the U.S. GovernmentPortfolio.

The U.S. Government Portfolio typically invests atleast 80% of its net assets (plus borrowings, if any) inobligations issued or guaranteed as to principal or inter-est by the U.S. government or its agencies andinstrumentalities, as well as repurchase agreementssecured by such instruments.

The Portfolio follows a disciplined investmentprocess that attempts to provide stability of principal,liquidity and current income, by investing in U.S. gov-ernment securities and other high quality money market

instruments. Among other things, the Adviser conductsits own credit analyses of potential investments andportfolio holdings, and relies substantially on a dedi-cated short-term credit research team. The Portfolioinvests in accordance with regulatory requirementsapplicable to money market funds, which require,among other things, the Portfolio to invest only in short-term, high quality debt obligations (generally, securitiesthat have remaining maturities of 397 calendar days orless and either have been rated in one of the two highestshort-term rating categories or are considered by thePortfolio to be of comparable quality), to maintain amaximum dollar-weighted average maturity of 60 daysor less, and to meet requirements as to portfoliodiversification and liquidity. All securities held by thePortfolio are U.S. dollar-denominated, and they mayhave fixed, variable or floating interest rates.


• Obligations issued or guaranteed as to principalor interest by the U.S. government or its agen-cies and instrumentalities, such as U.S. Treasurysecurities and securities issued by GNMA,which are backed by the full faith and credit ofthe United States;

• Obligations issued or guaranteed by the FederalHome Loan Mortgage Corporation, the FederalNational Mortgage Association, and U.S.government-sponsored entities such as the FederalHome Loan Bank, which are not backed by thefull faith and credit of the United States; and

• Repurchase agreements with respect to U.S.government securities

TREASURY FUND


The Treasury Fund invests substantially all of itsinvestable assets in the Treasury Portfolio.

The Treasury Portfolio attempts to meet its invest-ment objective by investing at least 80% of its net assetsin U.S. Treasury bills, notes and bonds (which are directobligations of the U.S. government). Under normalconditions, the Portfolio will invest substantially all ofits assets in such securities. The Portfolio also mayinvest in shares of other money market funds, includingfunds advised by the Adviser.

The Portfolio invests in accordance with regulatoryrequirements applicable to money market funds, which

23

require, among other things, the Portfolio to invest onlyin short-term securities (generally, securities that haveremaining maturities of 397 calendar days or less), tomaintain a maximum dollar weighted average maturityof 60 days or less, and to meet requirements as toportfolio diversification and liquidity.

TREASURY PLUS FUND


The Treasury Plus Fund invests substantially all ofits investable assets in the Treasury Plus Portfolio.

The Treasury Plus Portfolio attempts to meet itsinvestment objective by investing, under normalcircumstances, at least 80% of its net assets in U.S.Treasury bills, notes and bonds (which are direct obliga-tions of the U.S. government) and repurchase agree-ments collateralized by these obligations. The Portfolioalso may invest in shares of other money market funds,including funds advised by the Adviser.


Additional Information About Risks

Risk information is applicable to all Funds unlessotherwise noted.

• Money Market Risk. An investment in theFunds is not a deposit of any bank and is notinsured or guaranteed by the FDIC or any othergovernment agency. Although the Funds seek topreserve the value of your investment at $1.00per share, there can be no assurance that theywill do so, and it is possible to lose money byinvesting in the Funds.

• Interest Rate Risk. The values of debt instru-ments usually rise and fall in response tochanges in interest rates. Declining interest ratesgenerally result in increases in the values ofexisting debt instruments, and rising interestrates generally result in declines in the values ofexisting debt instruments. Interest rate risk isgenerally greater for investments with longer

durations or maturities. Some investments givethe issuer the option to call or redeem aninvestment before its maturity date. If an issuercalls or redeems an investment during a time ofdeclining interest rates, a Portfolio might have toreinvest the proceeds in an investment offering alower yield and therefore might not benefit fromany increase in value as a result of declininginterest rates. Adjustable rate instruments alsogenerally increase or decrease in value inresponse to changes in interest rates, althoughgenerally to a lesser degree than fixed-incomesecurities (depending, however, on thecharacteristics of the reset terms, including theindex chosen, frequency of reset, and reset capsor floors, among other factors). When interestrates decline, the income received by a Portfoliomay decline, and such Portfolio’s yield may alsodecline.

• Credit Risk (All Funds except the TreasuryFund). Credit risk is the risk that an issuer,guarantor or liquidity provider of a fixed-incomesecurity held by a Portfolio may be unable orunwilling, or may be perceived (whether bymarket participants, ratings agencies, pricingservices or otherwise) as unable or unwilling, tomake timely principal and/or interest payments,or to otherwise honor its obligations. It includesthe risk that one or more of the securities will bedowngraded by a credit rating agency; generally,lower credit quality issuers have higher creditrisks. An actual or perceived loss increditworthiness of an issuer of a fixed-incomesecurity held by a Portfolio may result in adecrease in the value of the security. Credit riskalso includes the risk that an issuer or guarantorof a security, or a bank or other financialinstitution that has entered into a repurchaseagreement with a Portfolio, may default on itspayment or repurchase obligation, as the casemay be.

• Liquidity Risk. Liquidity risk exists when par-ticular investments cannot be disposed ofquickly in the normal course of business. Theability of a Portfolio to dispose of such securitiesat advantageous prices may be greatly limited,and a Portfolio may have to continue to holdsuch securities during periods when the Adviserwould otherwise have sold them. Some secu-rities held by a Portfolio may be restricted as toresale, and there is often no ready market forsuch securities. In addition, a Portfolio, by itself

24

or together with other accounts managed by theAdviser, may hold a position in a security that islarge relative to the typical trading volume forthat security, which can make it difficult for thePortfolio to dispose of the position at anadvantageous time or price. Market values forilliquid securities may not be readily available,and there can be no assurance that any fair valueassigned to an illiquid security at any time willaccurately reflect the price a Portfolio mightreceive upon the sale of that security. It is possi-ble that, during periods of extreme market vola-tility or unusually high and unanticipated levelsof redemptions, a Portfolio may be forced to selllarge amounts of securities more quickly than itnormally would in the ordinary course ofbusiness. In such a case, the sale proceedsreceived by a Portfolio may be substantially lessthan if the Portfolio had been able to sell thesecurities in more-orderly transactions, and thesale price may be substantially lower than theprice previously used by the Portfolio to valueits securities.

• Stable Share Price Risk: If the market value ofone or more of a Portfolio’s investments changessubstantially, the Fund investing in such Portfo-lio may not be able to maintain a stable shareprice of $1.00. This risk typically is higher dur-ing periods of rapidly changing interest rates orwhen issuer credit quality generally is falling,and is made worse when a Portfolio experiencessignificant redemption requests.

• Master/Feeder Structure Risk. Unlike tradi-tional mutual funds that invest directly in secu-rities, each of the Funds pursues its objective byinvesting substantially all of its assets in aPortfolio with substantially the same investmentobjectives, policies and restrictions. The abilityof a Fund to meet its investment objective isdirectly related to the ability of the correspond-ing Portfolio to meet its objective. The ability ofa Fund to meet its objective may be adverselyaffected by the purchase and redemption activ-ities of other investors in the correspondingPortfolio and any related disruption to suchPortfolio’s investment program. The ability of aFund to meet redemption requests depends on itsability to redeem its interest in the correspondingPortfolio. The Adviser also serves as investmentadviser to the corresponding Portfolio. There-fore, conflicts may arise as the Adviser fulfills

its fiduciary responsibilities to a Fund and itscorresponding Portfolio. For example, theAdviser may have an economic incentive tomaintain a Fund’s investment in the correspond-ing Portfolio at a time when it might otherwisenot choose to do so.

• Low Short-Term Interest Rate Risk: At the dateof this Prospectus, short-term interest rates are athistorically low levels, and so each Fund’s yieldis very low. It is possible that a Portfolio willgenerate an insufficient amount of income to payits expenses, and that it and/or a Fund will not beable to pay a daily dividend and may have a neg-ative yield (i.e., it may lose money on an operat-ing basis). It is possible that a Portfolio willmaintain a substantial portion of its assets in cash,on which it would earn little, if any, income.

• Market Risk. The values of the securities inwhich a Portfolio invests may go up or down inresponse to the prospects of individual issuersand/or general economic conditions. Pricechanges may be temporary or may last forextended periods. Recent instability in thefinancial markets has led the U.S. Governmentto take a number of unprecedented actionsdesigned to support certain financial institutionsand segments of the financial markets that haveexperienced extreme volatility and, in somecases, a lack of liquidity. Federal, state, andother governments, their regulatory agencies, orself regulatory organizations may take actionsthat affect the regulation of the instruments inwhich the Portfolios invest, or the issuers ofsuch instruments, in ways that are unforeseeable.Legislation or regulation may also change theway in which the Funds and Portfoliosthemselves are regulated. Such legislation orregulation could limit or preclude a Fund’s orPortfolio’s ability to achieve its investmentobjective. Furthermore, volatile financialmarkets can expose the Portfolios to greatermarket and liquidity risk and potential difficultyin valuing portfolio instruments held by thePortfolios.

• Money Market Fund Regulatory Risk: It ispossible that the SEC or another agency willadopt regulations that change in very importantrespects the operation of money market funds.Any such regulatory changes could impactimportant characteristics of the Fund, including

25

liquidity of an investment in the Fund or theFund’s ability to maintain a stable net assetvalue per share.

• Repurchase Agreement Risk (ILR Fund, TaxFree Fund, U.S. Government Fund andTreasury Plus Fund only). In a repurchaseagreement, a Portfolio purchases a security froma seller at one price and simultaneously agrees tosell it back to the original seller at an agreed-upon price. Repurchase agreements may beviewed as loans made by the Portfolio which arecollateralized by the securities subject torepurchase. A Portfolio’s investment return onsuch transactions will depend on the counter-parties’ willingness and ability to perform theirobligations under the repurchase agreements. Ifa Portfolio’s counterparty should default on itsobligations and the Portfolio is delayed or pre-vented from recovering the collateral, or if thevalue of the collateral is insufficient, the Portfo-lio may realize a loss.

• U.S. Government Securities Risk (ILR Fund,U.S. Government Fund and Treasury Plus Fundonly). U.S. Government securities include avariety of securities (including U.S. Treasurybills, notes, and bonds) that differ in their inter-est rates, maturities, and dates of issue. Whilesecurities issued or guaranteed by the U.S.Treasury and some agencies or instrumentalitiesof the U.S. Government (such as the Govern-ment National Mortgage Association) are sup-ported by the full faith and credit of the UnitedStates, securities issued or guaranteed by certainother agencies or instrumentalities of the U.S.Government (such as Federal Home LoanBanks) are supported by the right of the issuer toborrow from the U.S. Government, and secu-rities issued or guaranteed by certain otheragencies and instrumentalities of the U.S. Gov-ernment (such as Fannie Mae and Freddie Mac)are supported only by the credit of the issueritself. Investments in these securities are alsosubject to interest rate risk and prepayment risk,and the risk that the value of the securities willfluctuate in response to political, market, oreconomic developments.

• Variable and Floating Rate Securities (ILRFund, Tax Free Fund and U.S. GovernmentFund only). In addition to traditional fixed-ratesecurities, a Portfolio may invest in debt secu-rities with variable or floating interest rates or

dividend payments. Variable or floating ratesecurities bear rates of interest that are adjustedperiodically according to formulae intended toreflect market rates of interest. Variable orfloating rate securities allow a Portfolio toparticipate in increases in interest rates throughupward adjustments of the coupon rates on suchsecurities. However, during periods of increas-ing interest rates, changes in the coupon ratesmay lag the change in market rates or may havelimits on the maximum increase in coupon rates.Alternatively, during periods of declining inter-est rates, the coupon rates on such securitiesreadjust downward resulting in a lower yield.

• Mortgage-Related and Asset-Backed SecuritiesRisk (ILR Fund and U.S. Government Fundonly). Mortgage-related securities represent aparticipation in, or are secured by, mortgageloans. Asset-backed securities are typicallystructured like mortgage-related securities, butinstead of mortgage loans or interests in mort-gage loans, the underlying assets may includesuch items as motor vehicle installment sales orinstallment loan contracts, leases on varioustypes of real and personal property, and receiv-ables from credit card agreements. During peri-ods of falling interest rates, mortgage-relatedand asset-backed securities, which typicallyprovide the issuer with the right to prepay thesecurity prior to maturity, may be prepaid, whichmay result in a Portfolio having to reinvest theproceeds in other investments at lower interestrates. During periods of rising interest rates, theaverage life of mortgage-related and asset-backed securities may extend because of slower-than expected principal payments. This maylock in a below market interest rate, increase thesecurity’s duration and volatility, and reduce thevalue of the security. As a result, mortgage-related and asset-backed securities may haveless potential for capital appreciation duringperiods of declining interest rates than othersecurities of comparable maturities, althoughthey may have a similar risk of decline in marketvalues during periods of rising interest rates.Prepayment rates are difficult to predict and thepotential impact of prepayments on the value ofa mortgage-related or an asset-backed securitydepends on the terms of the instrument and canresult in significant volatility. The price of amortgage-related or asset-backed security alsodepends on the credit quality and adequacy of

26

the underlying assets or collateral, if any.Defaults on the underlying assets, if any, mayimpair the value of an asset-backed or amortgage-related security. For some asset-backed securities in which a Portfolio invests,such as those backed by credit card receivables,the underlying cash flows may not be supportedby a security interest in a related asset. More-over, the values of mortgage-related and asset-backed securities may be substantiallydependent on the servicing of the underlyingasset pools, and are therefore subject to risksassociated with the negligence or malfeasanceby their servicers and to the credit risk of theirservicers. In certain situations, the mishandlingof related documentation may also affect therights of securities holders in and to the under-lying collateral, if any. Furthermore, there maybe legal and practical limitations on the enforce-ability of any security interest granted withrespect to underlying assets, or the value of theunderlying assets, if any, may be insufficient ifthe issuer defaults.

In a “forward roll” transaction, a Portfolio willsell a mortgage-related security to a bank orother permitted entity and simultaneously agreeto purchase a similar security from theinstitution at a later date at an agreed-upon price.The mortgage securities that are purchased willbear the same interest rate as those sold, butgenerally will be collateralized by differentpools of mortgages with different prepaymenthistories than those sold. Risks of mortgage-related security rolls include: the risk ofprepayment prior to maturity and the risk thatthe market value of the securities sold by thePortfolio may decline below the price at whichthe Portfolio is obligated to purchase thesecurities. Forward roll transactions may havethe effect of creating investment leverage in thePortfolio.

• Prepayment Risk and Extension Risk (ILR Fundand U.S. Government Fund only). Prepaymentrisk and extension risk apply primarily tomortgage-related and other asset-backed securities.

Prepayment risk is the risk that principal on loanobligations underlying a security may be repaidprior to the stated maturity date. If the Portfoliohas purchased a security at a premium, anyrepayment that is faster than expected reducesthe market value of the security and the

anticipated yield-to-maturity. Repayment ofloans underlying certain securities tends toaccelerate during periods of declining interestrates.

Extension risk is the risk that an issuer willexercise its right to repay principal on anobligation held by the Portfolio later thanexpected. This may happen when there is a risein interest rates, which could extend the durationof obligations held by the Portfolio and make thevalues of such obligations more sensitive tochanges in interest rates.

• Banking Industry Risk (ILR Fund only). If thePortfolio concentrates its investments in bankobligations, adverse developments in the bank-ing industry may have a greater effect on thePortfolio than on a mutual fund that investsmore broadly. Banks may be particularly sensi-tive to certain economic factors such as interestrate changes, adverse developments in the realestate market, fiscal and monetary policy andgeneral economic cycles. Recent instability inthe financial markets has heavily influenced theobligations of certain banking institutions,resulting in some cases in extreme price vola-tility and a lack of liquidity.

• Foreign Securities Risk (ILR Fund only). ThePortfolio may invest in U.S. dollar-denominatedobligations issued by non-U.S. issuers. Whilesuch instruments may be denominated in U.S.dollars, this does not eliminate the risk inherentin investing in the securities of foreign issuers.Dollar-denominated instruments issued by enti-ties located in foreign countries could lose valueas a result of political, financial and economicevents in foreign countries. Issuers of theseinstruments are not necessarily subject to thesame regulatory requirements that apply to U.S.banks and corporations, although theinformation available for dollar-denominatedinstruments may be subject to the accounting,auditing and financial reporting standards of theU.S. domestic market or exchange on whichthey are traded, which standards may be moreuniform and more exacting than those to whichmany foreign issuers are subject. Foreign banks,including those issuing instruments such asECDs, ETDs and YCDs, or their domestic orforeign branches, may be subject to less rigorousregulation than U.S. banks operating in theUnited States, and may not be required to meet

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financial, capital, and other requirements appli-cable to U.S. banks. Foreign laws and account-ing standards typically are not as strict as theyare in the U.S. so there may be fewer restrictionson loan limitations, less frequent examinationsand less stringent requirements regarding reserveaccounting, auditing, recordkeeping and publicreporting requirements.

• Section 4(2) Commercial Paper and Rule 144ASecurities Risk (ILR Fund only). The Portfoliomay invest in commercial paper issued in reli-ance on the private placement exemption fromregistration afforded by Section 4(2) of theSecurities Act of 1933, as amended (the “1933Act”). This commercial paper is commonlycalled “Section 4(2) paper.” The Portfolio mayalso invest in securities that may be offered andsold only to “qualified institutional buyers”under Rule 144A of the 1933 Act (“Rule 144Asecurities”).

Section 4(2) paper is sold to institutionalinvestors who must agree to purchase the paperfor investment and not with a view to publicdistribution. Any resale by the purchaser mustbe in a transaction exempt from the registrationrequirements of the 1933 Act. Section 4(2) papernormally is resold to other institutional investorslike the Portfolio through or with the assistanceof the issuer or investment dealers that make amarket in Section 4(2) paper. As a result itsuffers from liquidity risk, the risk that thesecurities may be difficult to value because ofthe absence of an active market and the risk thatit may be sold only after considerable expenseand delay, if at all. Rule 144A securitiesgenerally must be sold only to other qualifiedinstitutional buyers.

Section 4(2) paper and Rule 144A securities willnot be considered illiquid for purposes of aPortfolio’s limitation on illiquid securities if theAdviser (pursuant to guidelines adopted by theBoard) determines that a liquid trading marketexists for the securities in question. There can beno assurance that a liquid trading market willexist at any time for any particular Section 4(2)paper or Rule 144A securities. The Statement ofAdditional Information (“SAI”) addresses theFund’s and Portfolio’s limitation on illiquidsecurities.

• Municipal Securities Risk (Tax Free Fundonly). Municipal securities may be issued toobtain funds to be used for various public pur-poses, including general purpose financing forstate and local governments, refunding out-standing obligations, and financings for specificprojects or public facilities. General obligationsare backed by the full faith and credit of theissuer. These securities include, for example, taxanticipation notes, bond anticipation notes andgeneral obligation bonds. Revenue obligationsare generally backed by the revenues generatedfrom a specific project or facility and includeindustrial development bonds and private activ-ity bonds. Private activity and industrialdevelopment bonds are dependent on the abilityof the facility’s user to meet its financial obliga-tions and the value of any real or personal prop-erty pledged as security for such payment.Private activity and industrial developmentbonds, although issued by industrial develop-ment authorities, may be backed only by theassets of the non-governmental user. Municipalnotes are short-term instruments which areissued and sold in anticipation of a bond sale,collection of taxes or receipt of other revenues.

Some municipal securities are insured by privateinsurance companies, while others may besupported by letters of credit furnished bydomestic or foreign banks. In determining thecredit quality of insured or letter of credit-backed securities, the Adviser reviews thefinancial condition and creditworthiness of suchparties including insurance companies, banksand corporations.

Unlike most other bonds, however, municipalbonds pay interest that is exempt from federalincome taxes and, in some cases, also from stateand local taxes. Municipal bonds, and municipalbond funds, can therefore be advantageous toinvestors in higher tax brackets. However,because the interest is tax-exempt, municipalbond yields typically are lower than yields ontaxable bonds and bond funds with comparablematurity ranges.

• Tax Exempt Commercial Paper (Tax Free Fundonly). Tax exempt commercial paper is ashort-term obligation with a stated maturity of365 days or less. It is typically issued to financeseasonal working capital needs or as short-termfinancing in anticipation of longer term financ-

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ing. Tax exempt commercial paper may be ageneral obligation that is backed by the full faithand credit of the issuer or it may be a revenueobligation that is backed by the revenues gen-erated from a specific project or facility. Eachinstrument may be backed only by the credit ofthe issuer or may be backed by some form ofcredit enhancement, typically in the form of aguarantee by a commercial bank.

ADDITIONAL INFORMATION ABOUT THEFUNDS’ AND PORTFOLIOS’ NON-PRINCIPALINVESTMENT STRATEGIES AND RISKS

The investments described below reflect theFunds’ and Portfolios’ current practices. In addition tothe principal risks described above, other risks aredescribed in some of the descriptions of the investmentsbelow:

Investment in other Investment Companies. APortfolio may invest in other money market funds thatare registered as investment companies under theInvestment Company Act of 1940, as amended (the“1940 Act”), including mutual funds and exchange-traded funds that are sponsored or advised by theAdviser or its affiliates, to the extent permitted byapplicable law or SEC exemptive relief. If a Portfolioinvests in other money market funds, shareholders of theFund will bear not only their proportionate share of theexpenses described in this Prospectus, but also,indirectly, the expenses, including, for example, advi-sory and administrative fees, of the money market fundsin which the Portfolio invests. Shareholders would alsobe exposed to the risks associated not only with theinvestments of the Portfolio (indirectly through theFund’s investment in the Portfolio) but also to theportfolio investments of the money market funds inwhich the Portfolio invests.

Temporary Defensive Positions. From time totime, a Portfolio may take temporary defensive posi-tions in attempting to respond to adverse market, eco-nomic or other conditions. Temporary defensivepositions may be taken, for example, to preserve capitalor if a Portfolio is unable to acquire the types of secu-rities in which it normally invests. Temporary defensivepositions may include, but are not limited to, investmentin U.S. government securities, repurchase agreementscollateralized by such securities, the maintenance ofuninvested cash, or investment in cash equivalents. APortfolio’s holdings in temporary defensive positionsmay be inconsistent with the Portfolio’s principal

investment strategy, and, as a result, the Portfolio maynot achieve its investment objective.

PORTFOLIO HOLDINGS DISCLOSURE

The Funds’ portfolio holdings disclosure policy isdescribed in the SAI.

MANAGEMENT AND ORGANIZATION

The Funds and the Portfolios. Each Fund is aseparate, diversified series of the State Street Institu-tional Investment Trust (the “Trust”), which is an open-end management investment company organized as abusiness trust under the laws of The Commonwealth ofMassachusetts.

Each Fund invests as part of a “master-feeder”structure. Each Fund currently seeks to achieve itsinvestment objective by investing substantially all of itsinvestable assets in a corresponding Portfolio, a separatemutual fund, that has a substantially identical invest-ment objective, investment policies, and risks as theFund. All discussions about a Fund’s investmentobjective, policies and risks should be understood torefer also to the investment objectives, policies and risksof the corresponding Portfolio.

A Fund can withdraw its investment in a Portfolioif, at any time, the Fund’s Board of Trustees determinesthat it would be in the best interests of the Fund’sshareholders, or if the investment objectives of thecorresponding Portfolio changed so that they wereinconsistent with the objectives of the Fund. If a Fundwithdraws its investment from a Portfolio, the Fund mayinvest all of its assets in another mutual fund that has thesame investment objective as the Fund, the Adviser maydirectly manage the Fund’s assets, or the Board maytake such other action it deems appropriate and in thebest interests of shareholders of the Fund, which mayinclude liquidation of the Fund.

The Adviser. State Street Global Advisors(“SSgA”) is the investment management group of StateStreet Corporation, a publicly held bank holding com-pany. SSgA is one of the world’s largest institutionalmoney managers, and uses quantitative and traditionaltechniques to manage approximately $2.09 trillion as ofDecember 31, 2012 in investment programs and portfo-lios for institutional and individual investors. SSgA FM,a wholly-owned subsidiary of State Street Corporationis the investment adviser to the Funds and the Portfolios,and is registered with the SEC under the Investment

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Advisers Act of 1940, as amended. SSgA FM hadapproximately $264.87 billion in assets under manage-ment at December 31, 2012. Each Fund has entered intoan investment advisory agreement with the Adviserpursuant to which the Adviser will manage the Fund’sassets directly, for compensation paid at an annual rateof 0.05% of the Fund’s average daily net assets, in theevent that the Fund were to cease investing substantiallyall of its assets in its corresponding Portfolio or anotherinvestment company with essentially the same invest-ment objectives and policies as the Fund. The Adviserdoes not receive any management fees from a Fundunder that agreement so long as the Fund continues toinvest substantially all of its assets in the correspondingPortfolio or in another investment company with essen-tially the same investment objectives and policies as theFund. For the year ended December 31, 2012, the effec-tive management fee paid, reflecting certain fee waiversand expense reimbursements of the Adviser, was0.050% for Money Market Portfolio, 0.000% for TaxFree Money Market Portfolio, 0.030% for U.S.Government Portfolio, 0.000% for Treasury Portfolioand 0.000% for Treasury Plus Portfolio. The Adviserand/or the Funds’ distributor, State Street Global Mar-kets, LLC, may reimburse expenses or waive fees inorder to avoid a negative yield. Any such waiver orreimbursement would be voluntary and may be revisedor cancelled at any time. The Adviser places all ordersfor purchases and sales of the portfolios’ investments. Inaddition to any contractual expense limitation for a Fundwhich is described in the Fund Summaries, the Adviseralso may voluntarily reduce all or a portion of its feesand/or reimburse expenses for a Fund to the extentnecessary to avoid negative yield which may vary fromtime to time and from Fund to Fund in the Adviser’ssole discretion. Under an agreement with the Adviserrelating to the Voluntary Reduction, the Funds haveagreed to reimburse the Adviser for the full dollaramount of any Voluntary Reduction beginning onOctober 1, 2012, subject to certain limitations. A Fundwill not be obligated to reimburse the Adviser: morethan three years after the end of the fiscal year for theFund in which the Adviser provided a VoluntaryReduction; in respect of any business day for which thenet annualized one-day yield is less than 0.00%; to theextent that the amount of the reimbursement to theAdviser on any day exceeds fifty percent of the yield(net of all expenses, exclusive of the reimbursement) ofthe Fund on that day; to the extent that the amount ofsuch reimbursement would cause the Fund’s net yield tofall below the Fund’s minimum net yield as determinedby the Advisor in its sole discretion; or in respect of anyfee waivers and/or expense reimbursements that are

necessary to maintain a Fund’s contractual total expenselimit which is effective at the time of such fee waiversand/or expense reimbursements. A reimbursement to theAdviser would increase fund expenses and negativelyimpact a Fund’s future yield. There is no guarantee thata Fund will be able to avoid a negative yield. TheAdviser may, in its sole discretion, irrevocably waivereceipt of any or all reimbursement amounts due from aFund, without limitation.

A summary of the factors considered by the Boardof Trustees in connection with the renewals of theinvestment advisory agreements for the Funds is avail-able in the Funds’ annual report to shareholders datedDecember 31, 2012.

The Adviser’s principal address is State StreetFinancial Center, One Lincoln Street, Boston,Massachusetts 02111.

The Administrator, Sub-Administrator and Cus-todian. Effective February 1, 2011, the Adviser servesas administrator of each Fund. The amount of the feepaid to the Adviser for administrative services varies byshare class. Each Fund pays the Adviser an admin-istrative fee at the annual rate of 0.05% in respect of itsInstitutional Class shares. Prior to February 1, 2011,State Street Bank and Trust Company (“State Street”), asubsidiary of State Street Corporation, served as admin-istrator of each Fund for an annual fee of $25,000.Effective February 1, 2011, State Street serves as thesub-administrator for the Funds for a fee that is paid bythe Adviser. State Street also serves as custodian of theFunds for a separate fee that is paid by each Fund.

The Transfer Agent and Dividend DisbursingAgent. Boston Financial Data Services, Inc. is thetransfer agent and dividend disbursing agent.

The Distributor. State Street Global Markets,LLC serves as the Funds’ distributor (the “Distributor”)pursuant to the Distribution Agreement between theDistributor and the Trust.

SHAREHOLDER INFORMATION

Determination of Net Asset Value. The Tax FreeFund determines its NAV per share once each businessday at 12:00 p.m. Eastern Time (“ET”) or the close ofthe New York Stock Exchange (the “NYSE”), which-ever is earlier. The Treasury Fund determines its NAVper share once each business day at 2:30 p.m. ET or the

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close of the NYSE, whichever is earlier. Each of theother Funds determines its NAV per share once eachbusiness day at 5:00 p.m. ET except for days when theNYSE closes earlier than its regular closing time, inwhich event those Funds will determine their NAVs atthe earlier closing time (the time when a Funddetermines its NAV per share is referred to herein as the“Valuation Time”). Pricing does not occur on NYSEholidays. A business day is one on which the NYSE isopen for regular trading. The Federal Reserve is closedon certain holidays on which the NYSE is open. Theseholidays are Columbus Day and Veterans Day. On theseholidays, you will not be able to purchase shares bywiring Federal Funds because Federal Funds wiringdoes not occur on days when the Federal Reserve isclosed.

Each of the Funds seeks to maintain a $1.00 pershare NAV and, accordingly, uses the amortized costvaluation method, in compliance with Rule 2a-7’s risklimiting conditions, to value its portfolio instruments.The amortized cost valuation method initially prices aninstrument at its cost and thereafter assumes a constantamortization to maturity of any discount or premium,regardless of the impact of fluctuating interest rates onthe market value of the instrument.

If you hold shares of a Fund through a broker-dealeror other financial intermediary, your intermediary mayoffer additional services and account features that are notdescribed in this Prospectus. Please contact yourintermediary directly for an explanation of these services.

Purchasing Shares. Investors pay no sales load toinvest in the Institutional Class of the Funds. The pricefor Fund shares is the NAV per share. Orders will bepriced at the NAV next calculated after the order isaccepted by the Funds.

Purchase orders in good form (a purchase requestis in good form if it meets the requirementsimplemented from time to time by the Funds’ transferagent or a Fund, and for new accounts includes sub-mission of a completed and signed application and alldocumentation necessary to open an account) on a busi-ness day will, if payment is received the same day byFed Wire before the close of the Federal Reserve, ifaccepted, receive that day’s NAV and will earn divi-dends declared on the date of the purchase. All pur-chases that are made by check will begin earningdividends the following business day after the day theorder is accepted. (If you purchase shares by check,your order will not be in good form until the Fund’s

transfer agent receives federal funds for the check.) Allpurchase orders are subject to acceptance by the Funds.The Funds intend to be as fully invested as is practi-cable; therefore, investments must be made in FederalFunds (i.e., monies credited to the account of the Funds’custodian bank by a Federal Reserve Bank).

The minimum initial investment in InstitutionalClass shares of the Funds is $25 million. Holdings ofrelated customer accounts may be aggregated for pur-poses of determining the minimum investment amount.“Related customer accounts” include accounts held bythe same investment or retirement plan, financialinstitution, broker, dealer or intermediary. The Fundsand the Adviser reserve the right to increase or decreasethe minimum amount required to open or maintain anaccount. There is no minimum subsequent investment,except in relation to maintaining certain minimumaccount balances (See “Redeeming Shares” below). TheFunds require prior notification of subsequent invest-ments in excess of: $5,000,000 for the Tax Free Fund;$10,000,000 for the Treasury Fund; and $50,000,000 forthe ILR Fund, U.S. Government Fund, and TreasuryPlus Fund.

The Funds reserve the right to cease acceptinginvestments at any time or to reject any investmentorder. In addition, the ILR Fund, U.S. Government Fundand the Treasury Plus Fund may limit the amount of apurchase order received after 3:00 p.m. ET. The Treas-ury Fund may limit the amount of a purchase orderreceived after 12:00 p.m. (noon) ET.

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How to Purchase Shares

By Mail:

An initial investment in the Funds must be preceded oraccompanied by a completed, signed Institutional Account Appli-cation Form, sent to:

State Street Institutional Trust FundsP.O. Box 8048Boston, MA 02266-8048

By Overnight:

State Street Institutional Trust Funds30 Dan RoadCanton, MA 02021-2809

By Telephone/Fax:

An initial investment in the Funds must be preceded or accom-panied by a completed, signed Institutional Account ApplicationForm, faxed to (816) 218-0400. Call the Fund at (866) 392-0869between the hours of 8:00 a.m. ET and 5:00 p.m. ET to:

➣ confirm receipt of the faxed Institutional AccountApplication Form (initial purchases only),

➣ request your new account number (initial purchases only),➣ confirm the amount being wired and wiring bank, and➣ receive a confirmation number for your purchase order

(your trade is not effective until you have received aconfirmation number from the Fund).

For your initial investment, send the original, signed InstitutionalAccount Application Form to the address above.

Wire Instructions:

Instruct your bank to transfer money by Federal Funds wire to:State Street Bank andTrust Company2 Avenue de LafayetteBoston, MA 02111

ABA# 011000028DDA# 9905-801-8State Street Institutional Investment TrustFund nameInstitutional ClassAccount NumberAccount Registration

On Columbus Day and Veterans Day, you will not be able topurchase shares by wiring Federal Funds because the FederalFunds wiring does not occur on those days. Payment for Fundshares must be in Federal Funds (or converted to Federal Funds bythe Transfer Agent) by the close of the Federal Reserve.

You will not be able to redeem shares from the accountuntil the original Application has been received. The Funds andthe Funds’ agents are not responsible for transfer errors by thesending or receiving bank and will not be liable for any lossincurred due to a wire transfer not having been received.

In accordance with certain federal regulations, theTrust is required to obtain, verify and recordinformation that identifies each entity that applies toopen an account. For this reason, when you open (orchange ownership of) an account, the Trust will requestcertain information, including your name, residential/business address, date of birth (for individuals) and

taxpayer identification number or other governmentidentification number and other information that willallow us to identify you which will be used to verifyyour identity. The Trust may also request to reviewother identification documents such as driver license,passport or documents showing the existence of thebusiness entity. If you do not provide sufficientinformation to verify your identity, the Trust will notopen an account for you. As required by law, the Trustmay employ various procedures, such as comparingyour information to fraud databases or requesting addi-tional information and documentation from you, toensure that the information supplied by you is correct.The Trust reserves the right to reject any purchase forany reason, including failure to provide the Trust withinformation necessary to confirm your identity asrequired by law.

Redeeming Shares. An investor may redeem allor any portion of its investment at the NAV nextdetermined after it submits a redemption request, inproper form, to the Funds. Redemption orders are proc-essed at the NAV next determined after a Fund receivesa redemption order in good form. If a Fund receives aredemption order prior to its Valuation Time on a busi-ness day, the Fund may send payment for redeemedshares on that day. No dividends will be paid on sharesthat are redeemed and wired the same day. Each Fund,other than the ILR Fund, reserves the right to pay forredeemed shares within seven days after receiving aredemption order if, in the judgment of the Adviser, anearlier payment could adversely affect the Fund. For theILR Fund, shares are redeemed, and payment forredeemed shares sent, no later than the next businessday.

The right of any investor to receive payment withrespect to any redemption may be suspended or thepayment of the redemption proceeds postponed duringany period in which the NYSE is closed (other thanweekends or holidays) or trading on the NYSE isrestricted or, to the extent otherwise permitted by the1940 Act, if an emergency exists as a result of whichdisposal by the Fund of securities owned by it is notreasonably practicable or it is not reasonably practicablefor the Fund fairly to determine the value of its netassets. In addition, the SEC may by order permitsuspension of redemptions for the protection of share-holders of the Funds. Although each Fund attempts tomaintain its NAV at $1.00 per share, there can be noassurance that it will be successful, and there can be noassurance that a shareholder will receive $1.00 per shareupon any redemption.

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A request for a partial redemption by an investorwhose account balance is below the minimum amountor a request for partial redemption by an investor thatwould bring the account below the minimum amountmay be treated as a request for a complete redemptionof the account. These minimums may be different forinvestments made through certain financial inter-mediaries as determined by their policies and may bewaived in the Adviser’s discretion. The Funds reservethe right to modify minimum account requirements atany time with or without prior notice. The Funds alsoreserve the right to involuntarily redeem an investor’saccount if the investor’s account balance falls below theapplicable minimum amount due to transaction activity.

How to Redeem Shares

By Mail Send a signed letter to:State Street Institutional Investment Trust FundsP.O. Box 8048Boston, MA 02266-8048

The letter should include information necessary toprocess your request as described below. The Fundmay require a medallion guarantee in certain cir-cumstances. See “Medallion Guarantees” below.

By Overnight State Street Institutional Investment Trust Funds30 Dan RoadCanton, MA 02021-2809

By Telephone Please Call (866) 392-0869 between the hours of8:00 a.m. and 5 p.m. ET.

The Funds will need the following information to process yourredemption request:

➣ name(s) of account owners;

➣ account number(s);

➣ the name of the Fund;

➣ your daytime telephone number; and

➣ the dollar amount or number of shares being redeemed.

On any day that the Funds calculate NAV earlierthan normal, the Funds reserve the right to adjust thetimes noted above for purchasing and redeeming shares.

Medallion Guarantees. Certain redemption req-uests must include a medallion guarantee for eachregistered account owner if any of the following apply:

➣ Your account address has changed within thelast 10 business days.

➣ Redemption proceeds are being transferred toan account with a different registration.

➣ A wire is being sent to a financial institutionother than the one that has been established onyour Fund account.

➣ Other unusual situations as determined by theFunds’ transfer agent.

All redemption requests regarding shares of theFunds placed after 4:00 p.m. ET (2:00 p.m. ET for theTreasury Fund) may only be placed by telephone or pre-established other means such as a transmission. TheFunds reserve the right to postpone payments forredemption requests received after 4:00 p.m. ET(2:00 p.m. ET for the Treasury Fund) until the nextbusiness day. The Funds reserve the right to waivemedallion guarantee requirements, require a medallionguarantee under other circumstances or reject or delayredemption if the medallion guarantee is not in goodform. Medallion guarantees may be provided by aneligible financial institution such as a commercial bank,a FINRA member firm such as a stock broker, a savingsassociation or a national securities exchange. A notarypublic cannot provide a medallion guarantee. The Fundsreserve the right to reject a medallion guarantee if it isnot provided by a STAMP Medallion guarantor.

About Telephone Transactions. Telephone trans-actions are extremely convenient but are not free fromrisk. Neither the Funds nor the Funds’ agents will beresponsible for any losses resulting from unauthorizedtelephone transactions if reasonable security proceduresare followed. In addition, you are responsible for:(i) verifying the accuracy of all data and informationtransmitted by telephone, (ii) verifying the accuracy ofyour account statements immediately upon receipt, and(iii) promptly notifying the Funds of any errors orinaccuracies including, without limitation, any errors orinaccuracies relating to shareholder data or informationtransmitted by telephone. During periods of heavymarket activity or other times, it may be difficult toreach the Funds by telephone. If you are unable to reachus by telephone, consider sending written instructions.

The Funds may terminate the receipt of redemptionorders by telephone at any time, in which case you mayredeem shares by other means.

If you choose to purchase or redeem shares bysending instructions by regular mail, they will not bedeemed received in good order until they are released bythe post office and redelivered to the Transfer Agent’sphysical location at 30 Dan Road in Canton, MA 02021.There will be a time lag, which may be one or more

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days, between regular mail receipt at the Boston postoffice box and redelivery to such physical location inCanton, and a Fund’s net asset value may change overthose days. You might consider using express ratherthan regular mail if you believe time of receipt of yourtransaction request to be sensitive.

Policies to Prevent Market Timing. Frequentpurchases and redemptions of Fund shares may presentrisks for other shareholders of the Funds, which mayinclude, among other things, interference in the efficientmanagement of a Fund’s portfolio, dilution in the valueof shares held by long-term shareholders, increasedbrokerage and administrative costs and forcing theFunds to hold excess levels of cash.

The Trust’s Board of Trustees has adopted policiesand procedures designed to detect and preventinappropriate short-term trading activity that is harmfulto the Funds. Because most of the shares of the Fundsare held by investors indirectly through one or morefinancial intermediaries, the Funds do not generallyhave information about the identity of those investors orabout transactions effected by those investors. Rather,the Funds and service providers to the Funds periodi-cally review cash inflows and outflows from and tothose intermediaries in an attempt to detectinappropriate trading activity by investors holdingshares through those intermediaries. The Funds mayseek to obtain underlying account trading activityinformation from financial intermediaries when, in theAdviser’s judgment, the trading activity suggests possi-ble market timing. There is no assurance that the Fundsor the Adviser will be able to determine whether tradingin the Funds’ shares by an investor holding sharesthrough a financial intermediary is trading activity thatmay be harmful to the Funds or the Funds’ shareholders.

The Funds reserve the right in their discretion toreject any purchase, in whole or in part, including,without limitation, by a person whose trading activity inFund shares the Adviser believes could be harmful tothe Funds. The Funds may decide to restrict purchaseactivity in their shares based on various factors, includ-ing, without limitation, whether frequent purchase andsale activity will disrupt portfolio management strat-egies or adversely affect performance. There can be noassurance that the Funds, the Adviser, State Street ortheir agents will identify all frequent purchase and saleactivity affecting the Funds.

PAYMENTS TO FINANCIAL INTERMEDIARIES

The Adviser, or an affiliate of the Adviser, out ofits own resources, and without additional cost to a Fundor its shareholders, may make additional payments tofinancial intermediaries (including affiliates of theAdviser) whose clients or customers invest in the Funds.Generally, such financial intermediaries may (thoughthey will not necessarily) provide shareholder servicingand support for their customers who purchase shares ofthe Funds. Not all financial intermediaries receive addi-tional compensation and the amount of compensationpaid varies for each financial intermediary. If paymentsto financial intermediaries by a particular mutual fundcomplex’s distributor or adviser exceed payments byother mutual fund complexes, your financial adviser andthe financial intermediary employing him or her mayhave an incentive to recommend that fund complex overothers. Please speak with your financial adviser to learnmore about the total amounts paid to your financialadviser and his or her firm by the Adviser and its affili-ates, and by sponsors of other mutual funds he or shemay recommend to you. You should also consult dis-closures made by your financial intermediary at the timeof purchase.

DIVIDENDS, DISTRIBUTIONS AND TAXCONSIDERATIONS

The Funds intend to declare dividends on sharesfrom net investment income daily and pay them as ofthe last business day of each month. Distributions fromcapital gains, if any, will be made annually inDecember.

The following discussion is a summary of someimportant U.S. federal tax considerations generallyapplicable to investments in the Funds. Your investmentin the Funds may have other tax implications. Pleaseconsult your tax advisor about foreign, federal, state,local or other tax laws applicable to you. Investors,including non-U.S. investors, should consult the SAI taxsection for more complete disclosure.

Each Fund has elected to be treated as a regulatedinvestment company and intends each year to qualifyand to be eligible to be treated as such. A regulatedinvestment company is generally not subject to tax atthe corporate level on income and gains that are dis-tributed to shareholders. However, a Fund’s failure toqualify as a regulated investment company would resultin corporate level taxation, and consequently, a reduc-tion in income available for distribution to shareholders.

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For federal income tax purposes, distributions ofinvestment income (other than “exempt-interest divi-dends” described below) are generally taxable to you asordinary income. Taxes on distributions of capital gainsgenerally are determined by how long the applicablePortfolio owned the investments that generated them,rather than how long you have owned your Fund shares.The Funds generally do not expect to make distributionsthat are eligible for taxation as long-term capital gains.

Distributions from the Tax Free Fund properlyreported as “exempt-interest dividends” are not gen-erally subject to federal income tax, including thefederal alternative minimum tax for individuals, butmay be included in “adjusted current earnings” forpurposes of the federal alternative minimum tax forcorporate shareholders and may be subject to state andlocal taxes. If you receive Social Security or railroadretirement benefits, you should consult your tax advisorto determine what effect, if any, an investment in theTax Free Fund may have on the federal taxation of yourbenefits. Distributions of the Tax Free Fund’s incomeother than exempt-interest dividends generally will betaxable as ordinary income, and distributions of the TaxFree Fund’s net long-term and short-term capital gains(if any) generally will be taxable to you as long-term orshort-term capital gain, as applicable, including inrespect of gains generated from the sale or other dis-position of tax-exempt municipal obligations. The TaxFree Portfolio may also invest a portion of its assets insecurities that generate income (that will be allocated toand distributed by the Fund) that will be subject to bothfederal and state taxes.

Distributions (other than distributions of exempt-interest dividends) are taxable whether you receive themin cash or reinvest them in additional shares. Any gainsresulting from the redemption of Fund shares will gen-erally be taxable to you as either short-term or long-termcapital gain, depending upon how long you have heldyour shares in the Fund.

Effective for taxable years beginning on or afterJanuary 1, 2013, a 3.8% Medicare contribution tax isimposed on the “net investment income” of individuals,estates and trusts whose income exceeds certain thresh-old amounts. Net investment income generally includesfor this purpose dividends paid by a Fund, including anycapital gain dividends, and net capital gains recognizedon the redemption of shares of a Fund.

If you are not a citizen or permanent resident of theUnited States, each Fund’s ordinary income dividends,

but not its exempt-interest dividends, will generally besubject to a 30% U.S. withholding tax, unless a lowertreaty rate applies or unless such income is effectivelyconnected with a U.S. trade or business. For taxableyears of the Funds beginning before January 1, 2014, aFund is able, under certain circumstances, to report in awritten notice to shareholders all or a portion of a divi-dend as an “interest-related dividend” or a “short-termcapital gain dividend” that if received by a nonresidentalien or foreign entity generally is exempt from the 30%U.S. withholding tax, provided that certain otherrequirements are met. These exemptions will expire fordistributions with respect to taxable years of a Fundbeginning on or after January 1, 2014, unless Congressenacts legislation providing otherwise.

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FINANCIAL HIGHLIGHTS

The Financial Highlights table is intended to help you understand the financial performance of the ILR Fund,the Tax Free Fund, the U.S. Government Fund, the Treasury Fund, and the Treasury Plus Fund, for the past fiveyears. Certain information reflects financial results for a single Institutional Class share of each Fund. The totalreturn in the table represents the rate that an investor would have earned (or lost) on an investment in InstitutionalClass shares of each Fund (assuming reinvestment of all dividends and distributions). This information has beenaudited by Ernst & Young LLP, whose report, along with each listed Fund’s financial statements, is included in theFunds’ annual report, which is available upon request. The financial information included in this table should beread in conjunction with the financial statements incorporated by reference in the SAI.

36


Financial Highlights — Selected data for a share of beneficial interest outstanding throughout each period ispresented below(a):

Period Ended December 31,

Net AssetValue

Beginningof Period

NetInvestment

Income/(Loss)

Gain(Loss) on

Investments

Total fromInvestmentOperations

Distributionsfrom Net

InvestmentIncome

Distributionsfrom

Capital GainsTotal

Distributions

Liquid Reserves FundInstitutional Class

2012 $1.0000 $0.0020 $ 0.0000(d) $0.0020 $(0.0020) $(0.0000)(d) $(0.0020)2011 $1.0000 $0.0015 $ 0.0000(d) $0.0015 $(0.0015) $ – $(0.0015)2010 $1.0000 $0.0019 $ 0.0000(d) $0.0019 $(0.0019) $ – $(0.0019)2009 $1.0000 $0.0049 $ 0.0000(d) $0.0049 $(0.0049) $ – $(0.0049)2008 $1.0000 $0.0278 $ 0.0000(d) $0.0278 $(0.0278) $ – $(0.0278)

Tax Free Money Market FundInstitutional Class

2012 $1.0000 $0.0000(d) $ – $0.0000(d) $(0.0000)(d) $ – $(0.0000)(d)

2011 $1.0000 $0.0002 $(0.0000)(d) $0.0002 $(0.0002) $ – $(0.0002)2010 $1.0000 $0.0007 $ 0.0003 $0.0010 $(0.0008) $(0.0002) $(0.0010)2009 $1.0000 $0.0043 $ 0.0000(d) $0.0043 $(0.0043) $ – $(0.0043)2008 $1.0000 $0.0229 $ 0.0000(d) $0.0229 $(0.0229) $ – $(0.0229)

U.S. Government Money Market FundInstitutional Class

2012 $1.0000 $0.0003 $ 0.0000(d) $0.0003 $(0.0003) $ – $(0.0003)2011 $1.0000 $0.0002 $(0.0000)(d) $0.0002 $(0.0002) $ – $(0.0002)2010 $1.0000 $0.0007 $ 0.0000 $0.0007 $(0.0007) $ – $(0.0007)2009 $1.0000 $0.0025 $ 0.0001 $0.0026 $(0.0026) $ – $(0.0026)2008 $1.0000 $0.0215 $ – $0.0215 $(0.0215) $ – $(0.0215)

(a) The per share amounts and percentages include the Fund’s proportionate share of income and expenses of their corresponding Portfolio.(b) Total return is calculated assuming a purchase of shares at the net asset value on the first day and a sale at the net asset value on the last

day of each period reported. Distributions are assumed, for the purpose of this calculation, to be reinvested at the net asset value per shareon the respective payment dates. Total returns for periods of less than one year are not annualized. Results represent past performanceand are not indicative of future results.

(c) This expense waiver is reflected in both the net expense and the net income ratios shown above. Without these waivers, net investmentincome would have been lower.

(d) Amount is less than $0.00005 per share.(e) Amount is less than 0.005%.

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Net AssetValueEnd ofPeriod

Ratios to Average Net Assets/Supplemental Data(a)

Net AssetsEnd of Period(000s omitted)

TotalReturn(b)

GrossExpenses

NetExpenses

NetInvestment

IncomeExpenseWaiver(c)

Liquid Reserves FundInstitutional Class

2012 $1.0000 0.20% 0.12% 0.12% 0.20% – $24,408,8022011 $1.0000 0.15% 0.12% 0.12% 0.15% – $19,597,2642010 $1.0000 0.19% 0.12% 0.12% 0.20% 0.00%(e) $25,211,4882009 $1.0000 0.49% 0.14% 0.14% 0.43% 0.00%(e) $14,508,4092008 $1.0000 2.82% 0.11% 0.11% 2.78% – $ 7,774,494

Tax Free Money Market FundInstitutional Class

2012 $1.0000 0.00%(e) 0.20% 0.12% 0.00%(e) 0.08% $ 140,2552011 $1.0000 0.02% 0.19% 0.12% 0.02% 0.07% $ 87,1352010 $1.0000 0.10% 0.17% 0.17% 0.07% 0.00%(e) $ 114,4042009 $1.0000 0.43% 0.19% 0.19% 0.33% – $ 99,9762008 $1.0000 2.31% 0.14% 0.14% 2.29% – $ 65,171

U.S. Government Money Market FundInstitutional Class

2012 $1.0000 0.03% 0.13% 0.12% 0.03% 0.01% $ 7,114,2132011 $1.0000 0.02% 0.12% 0.10% 0.02% 0.02% $ 5,139,7952010 $1.0000 0.07% 0.13% 0.12% 0.07% 0.01% $ 4,430,3272009 $1.0000 0.26% 0.13% 0.12% 0.21% 0.01% $ 2,879,2082008 $1.0000 2.17% 0.14% 0.14% 1.70% – $ 1,659,576

38


Financial Highlights — Selected data for a share of beneficial interest outstanding throughout each period ispresented below(a):


Net AssetValue

Beginningof Period

NetInvestment

Income/(Loss)

Gain(Loss) on

Investments

Total fromInvestmentOperations

Distributionsfrom Net

InvestmentIncome

Distributionsfrom

Capital GainsTotal

Distributions

Treasury Money Market FundInstitutional Class

2012 $1.0000 $0.0000(d) $ 0.0000(d) $0.0000(d) $ – $(0.0000)(d) $(0.0000)(d)

2011 $1.0000 $0.0001 $ 0.0000(d) $0.0001 $(0.0001) $ – $(0.0001)2010 $1.0000 $0.0002 $(0.0001) $0.0001 $(0.0001) $ – $(0.0001)2009 $1.0000 $0.0003 $ 0.0001 $0.0004 $(0.0004) $(0.0000)(d) $(0.0004)2008 $1.0000 $0.0123 $ 0.0000(d) $0.0123 $(0.0123) $(0.0000)(d) $(0.0123)

Treasury Plus Money Market FundInstitutional Class

2012 $1.0000 $0.0002 $ 0.0000(d) $0.0002 $(0.0002) $ – $(0.0002)2011 $1.0000 $0.0001 $ 0.0000(d) $0.0001 $(0.0001) $ – $(0.0001)2010 $1.0000 $0.0004 $(0.0000)(d) $0.0004 $(0.0004) $ – $(0.0004)2009 $1.0000 $0.0004 $ 0.0002 $0.0006 $(0.0006) $(0.0000)(d) $(0.0006)2008 $1.0000 $0.0154 $ 0.0000(d) $0.0154 $(0.0154) $ – $(0.0154)

(a) The per share amounts and percentages include the Fund’s proportionate share of income and expenses of their corresponding Portfolio.(b) Total return is calculated assuming a purchase of shares at the net asset value on the first day and a sale at the net asset value on the last

day of each period reported. Distributions are assumed, for the purpose of this calculation, to be reinvested at the net asset value per shareon the respective payment dates. Total returns for periods of less than one year are not annualized. Results represent past performanceand are not indicative of future results.

(c) This expense waiver is reflected in both the net expense and the net income ratios shown above. Without these waivers, net investmentincome would have been lower.

(d) Amount is less than $0.00005 per share.(e) Amount is less than 0.005%.

39


Net AssetValueEnd ofPeriod

Ratios to Average Net Assets/Supplemental Data(a)

Net AssetsEnd of Period(000s omitted)

TotalReturn(b)

GrossExpenses

NetExpenses

NetInvestment

IncomeExpenseWaiver(c)

Treasury Money Market FundInstitutional Class

2012 $1.0000 0.00%(e) 0.12% 0.08% 0.00%(e) 0.04% $10,151,0782011 $1.0000 0.01% 0.13% 0.03% 0.00%(e) 0.10% $ 9,426,3342010 $1.0000 0.01% 0.13% 0.11% 0.01% 0.02% $ 2,790,2672009 $1.0000 0.04% 0.13% 0.11% 0.03% 0.02% $ 1,581,5252008 $1.0000 1.24% 0.14% 0.13% 0.80% 0.01% $ 1,036,263

Treasury Plus Money Market FundInstitutional Class

2012 $1.0000 0.02% 0.14% 0.11% 0.02% 0.03% $ 2,203,1412011 $1.0000 0.01% 0.14% 0.06% 0.01% 0.08% $ 1,220,1592010 $1.0000 0.04% 0.15% 0.11% 0.04% 0.04% $ 811,1442009 $1.0000 0.06% 0.15% 0.13% 0.04% 0.02% $ 654,5432008 $1.0000 1.55% 0.16% 0.13% 0.92% 0.03% $ 737,637

40

For more information about the Funds:

The Funds’ SAI includes additional information about the Funds and is incorporated by reference into thisdocument. Additional information about the Funds’ investments is available in the Funds’ annual and semiannualreports to shareholders.

The SAI and the Funds’ annual and semi-annual reports are available, without charge, upon request. Share-holders in the Funds may make inquiries to the Funds to receive such information by calling State Street GlobalMarkets, LLC at (877) 521-4083 or by writing to the Funds, c/o State Street Global Markets, LLC, State StreetFinancial Center, One Lincoln Street, Boston, Massachusetts 02111-2900. The Funds’ website address is http://www.ssga.com/cash.

Information about the Funds (including the SAI) can be reviewed and copied at the Commission’s Public Refer-ence Room in Washington, D.C. Information on the operation of the Public Reference Room may be obtained bycalling the Commission at 1-202-942-8090. Reports and other information about the Funds are available free ofcharge on the EDGAR Database on the Commission’s Internet site at http://www.sec.gov. Copies of this informationalso may be obtained, after paying a duplicating fee, by electronic request at the following E-mail address:[email protected], or by writing the Commission’s Public Reference Section, Washington, D.C. 20549-1520.

SSgA Funds Management, Inc.STATE STREET FINANCIAL CENTERONE LINCOLN STREETBOSTON, MASSACHUSETTS 02111

SSITINSTPRO

The State Street Institutional Investment Trust’s Investment Company Act File Number is 811-09819.

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