TRS members include all full-time, part-time, and substitute Illinois public school personnel employed outside the city of Chicago in positions requiring certification by the Illinois State Board of Education. Persons employed in certain state agencies relating to education are also TRS members.

As of June 30, 2007, there were 160,317 active members, 94,879 inactive members entitled to but not receiving benefits in TRS, and 89,236 annuitants and beneficiaries receiving benefits. The average age of an active full-time/part-time member was 41. The average age of an annuitant was 69. As of June 30, 2007, the average annual retirement annuity was $40,128.