40 ILCS 5/8-210
To make the payments authorized by this Article, the board may keep and hold uninvested a sum not in excess of the amounts required to make such payments estimated to be due in the following 90 days. Such sum or any part thereof shall be kept on deposit only in any bank or savings and loan association authorized to do business. The amount which may be deposited in any such bank or savings and loan association shall not exceed 25% of its paid up capital and surplus.
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 5/8-210