40 ILCS 5/22-401
Any annuity and benefit fund, annuity and retirement fund or retirement system, heretofore or hereafter created by the legislature of the State of Illinois for the benefit of employees of the State or of any county, city, town, municipal corporation or body politic and corporate, located in the State of Illinois and functioning pursuant to legislative enactment, to which the State or any such county, city, town, municipal corporation or body politic and corporate is required to contribute by way of tax levies, appropriations from the corporate fund, or otherwise, and by whatever name such annuity and benefit fund, annuity and retirement fund or retirement system may be called, is hereby declared to be a pension fund and to be a body politic and corporate under the title specified in the law creating such fund, limited to the performance of the duties set out in the law creating such fund. The trustees of each fund are hereby declared to be the officials of such body politic and corporate, vested with the powers and duties set out in said law.
40 ILCS 5/22-401