40 ILCS 5/12-171
The board may keep as an available sum for the purpose of making payments for annuities and other benefits, such an amount as shall be estimated by the board as being necessary to meet the current disbursements for a period not to exceed 90 days. Such sum shall be kept on deposit in any bank or savings and loan association in this State organized under the laws thereof or under the laws of the United States, or with any trust company incorporated under the laws of this State; provided said bank, savings and loan association or trust company shall furnish adequate security for said sum; and provided further that the sum so deposited shall not exceed 25% of the paid-up capital and surplus of said bank, savings and loan association or trust company.
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 5/12-171