0001107414 2021-05-07 2021-05-07 0001107414 ssiit:S000071465Member 2021-05-07 2021-05-07 pure iso4217:USD 0001107414 false 2021-10-29 2021-10-29 497 2020-12-31 N-1A <div style="margin-top: 0pt; margin-bottom: 0pt; font-size: 16pt; font-family: times new roman; font-weight: bold; text-align: center;">State Street Institutional Investment Trust</div> <div style="margin-top: 12pt; margin-bottom: 0pt; font-size: 10pt; font-family: times new roman; font-weight: bold; text-align: center;">STATE STREET INCOME FUND</div> <div style="margin-top: 0pt; margin-bottom: 0pt; font-size: 10pt; font-family: times new roman; font-weight: bold; text-align: center;">(SSASX)</div> <div style="margin-top: 0pt; margin-bottom: 0pt; font-size: 10pt; font-family: times new roman; font-weight: bold; text-align: center;">(the “Fund”)</div> <div style="margin-top: 12pt; margin-bottom: 0pt; font-size: 10pt; font-family: times new roman; font-weight: bold; text-align: center;">SUPPLEMENT DATED NOVEMBER 1, 2021 TO THE PROSPECTUS</div> <div style="margin-top: 0pt; margin-bottom: 0pt; font-size: 10pt; font-family: times new roman; font-weight: bold; text-align: center;">AND SUMMARY PROSPECTUS, EACH DATED MAY 7, 2021,</div> <div style="margin-top: 0pt; margin-bottom: 0pt; font-size: 10pt; font-family: times new roman; font-weight: bold; text-align: center;">AS EACH MAY BE SUPPLEMENTED FROM TIME TO TIME</div> <div style="margin-top: 12pt; margin-bottom: 0pt; font-size: 10pt; font-family: times new roman;"><span style="font-style: italic;">Effective immediately, the Fund’s Prospectus and Summary Prospectus are revised as follows: </span></div> <div style="margin-top: 12pt; margin-bottom: 0pt; font-size: 10pt; font-family: times new roman;">All references to “Bloomberg Barclays” are replaced with “Bloomberg” and other references to “Barclays” are removed.</div> <div style="margin-top: 0pt; margin-bottom: 0pt; font-size: 16pt; font-family: times new roman; font-weight: bold; text-align: center;">State Street Institutional Investment Trust</div> <div style="margin-top: 12pt; margin-bottom: 0pt; font-size: 10pt; font-family: times new roman; font-weight: bold; text-align: center;">STATE STREET INCOME FUND</div> <div style="margin-top: 0pt; margin-bottom: 0pt; font-size: 10pt; font-family: times new roman; font-weight: bold; text-align: center;">(SSASX)</div> <div style="margin-top: 0pt; margin-bottom: 0pt; font-size: 10pt; font-family: times new roman; font-weight: bold; text-align: center;">(the “Fund”)</div> <div style="margin-top: 12pt; margin-bottom: 0pt; font-size: 10pt; font-family: times new roman; font-weight: bold; text-align: center;">SUPPLEMENT DATED NOVEMBER 1, 2021 TO THE PROSPECTUS</div> <div style="margin-top: 0pt; margin-bottom: 0pt; font-size: 10pt; font-family: times new roman; font-weight: bold; text-align: center;">AND SUMMARY PROSPECTUS, EACH DATED MAY 7, 2021,</div> <div style="margin-top: 0pt; margin-bottom: 0pt; font-size: 10pt; font-family: times new roman; font-weight: bold; text-align: center;">AS EACH MAY BE SUPPLEMENTED FROM TIME TO TIME</div> <div style="margin-top: 12pt; margin-bottom: 0pt; font-size: 10pt; font-family: times new roman;"><span style="font-style: italic;">Effective immediately, the Fund’s Prospectus and Summary Prospectus are revised as follows: </span></div> <div style="margin-top: 12pt; margin-bottom: 0pt; font-size: 10pt; font-family: times new roman;">All references to “Bloomberg Barclays” are replaced with “Bloomberg” and other references to “Barclays” are removed.</div> State Street Institutional Investment Trust 2021-05-07