40 ILCS 5/13-215
"Retirement annuity": A benefit payable as an annuity for service as an employee. The annuity shall be payable in equal monthly installments for life, except as otherwise provided in this Article, beginning in the month after the effective date of the annuity , which shall not be prior to the date of withdrawal nor more than one year prior to the date of the employee's application for the annuity. A pro rata amount of the annuity shall be paid for part of a month when the annuity begins after the first day of the month or ends before the last day of the month.
Notwithstanding the above, all retirement annuity payments first payable on or after January 1, 2008, shall begin the first of the month following the effective date of retirement.
Effective January 1, 2008, benefits are payable for the full month if the annuitant was alive on the first day of the month.
40 ILCS 5/13-215