40 ILCS 5/6-192
To pay annuities and benefits, the board may at all times keep uninvested a sum not in excess of the amount required for such payments which become due and payable within the following 90 days. Such sum or any part thereof, shall be kept on deposit in any bank or savings and loan association authorized to do business in this State. The amount which the board may deposit in any such bank or savings and loan association, however, shall not exceed 25% of the paid up capital and surplus of the bank or savings and loan association.
No bank or savings and loan association shall receive investment funds as permitted by this Section, unless it has complied with the requirements, other than the maximum deposit requirement, established pursuant to Section 6 of "An Act relating to certain investments of public funds by public agencies", approved July 23, 1943, as now or hereafter amended.
40 ILCS 5/6-192