40 ILCS 5/12-183
An actuarial valuation shall be made annually of the liabilities and reserves for present and prospective annuities and benefits, and beginning January 1, 2013 a general investigation shall be made and shall be completed every 5 years thereafter of the operating experience of the fund as to mortality, disability, retirement, marital status of employees, withdrawal from service without right to annuity, investment earnings and other factors of actuarial criteria.
Upon the basis of the annual actuarial valuation and quinquennial actuarial investigations, the actuary shall recommend the tables to be used in the annual valuations and in current operations including the prescribed rate of interest, and shall advise the board on any matters of actuarial character affecting the financial condition of the fund and its operations.
40 ILCS 5/12-183