The Illinois Municipal Retirement Fund (IMRF) was created by the Illinois General Assembly in 1939 to provide death, disability, and retirement benefits for employees of local governments and most public school districts. Since 1941, IMRF has partnered with local units of government to administer defined benefit, locally-funded pension plans relying on pooled investments. The fund started with five employers and $5,000 in assets. Today, IMRF provides pension services for 2,950 local employers; has more than 180,000 active, contributing members, 138,530 inactive members, and 93,262 retirees collecting benefits; and manages $24.9 billion in assets. A majority of IMRF member employees are also covered by Social Security. 

IMRF is governed by an eight-member Board of Trustees, four of whom are elected by employers, three by participating members, and one by retirees. Benefits for all of the local pension plans are established by state statute—with some flexibility for minor customizations—and can only be changed by state legislative action.