From the Federal TRIO Programs 50th Anniversary Fact Sheet on the Department of Education website:

The Upward Bound (UB) Program, the first Federal TRIO Program, was created under the authority of the Economic Opportunity Act of 1964, as amended. A year later, Talent Search (TS) was created as part of the Higher Education Act of 1965 to assist students applying for newly authorized federal financial aid for postsecondary education.

The TRIO name itself was born four years later when the Higher Education Act of 1965 was amended in 1968 to include the Special Services for Disadvantaged Students program—what is now called Student Support Services (SSS). UB, TS and SSS formed a trio of Federal programs designed to foster increased educational opportunity and attainment. Since 1968, the TRIO programs have been expanded to provide a wider range of services.

Today, nine TRIO programs are included under the TRIO umbrella, seven of which provide direct services to students. The 1972 amendments to the Higher Education Act created Educational Opportunity Centers (EOCs) to help adults select a postsecondary education program and obtain financial aid. Veterans Upward Bound (VUB) was also initiated in the 1972 as part of the Upward Bound program to serve returning Vietnam veterans. Amendments in 1986 added the Ronald E. McNair Postbaccalaureate Achievement Program (McNair) to foster doctoral degree attainment by students from underrepresented segments of society. In 1990, the Upward Bound Math and Science (UBMS) program was initiated as part of the Upward Bound program to address the need for specific instruction in the fields of mathematics and science.

TRIO also includes a training program for project directors and other staff of TRIO projects (Training Program for Federal TRIO Programs, which was authorized in 1976). The TRIO programs are administered by the Student Service area of the Department’s Office of Postsecondary Education.

Source: US Department of Education

Additional information on the history of the TRIO federal grant program is available from the Council for Opportunity in Education.