40 ILCS 5/14-113
A member entitled to a retirement annuity may elect, at the time of retirement, to receive a lesser amount of such allowance and provide with the remainder of his equity, as actuarially determined, an annuity for any person who is dependent upon the member at the time of retirement, as named in a written direction filed with the board as a part of his application for a retirement annuity; provided, that (1) the condition of dependency exists and is proved to the satisfaction of the board; and that (2) the reversionary annuity resulting from such election is not less than $10 per month, nor more than the amount of reduced retirement annuity which the member receives under this option.
The reversionary annuity shall be the amount determined by the board in accordance with the member's written direction. A reversionary annuity shall begin the first day of the month following the death of the annuitant; provided, that if the designated reversionary annuity beneficiary does not survive the annuitant, a reversionary annuity shall not be payable nor shall any change be permitted in the written direction filed with the board after the retirement annuity has been granted and became effective.
40 ILCS 5/14-113