40 ILCS 5/12-128
A service annuity shall be provided for future entrants and present employees.
A prior service annuity shall be provided for present employees. A widow's prior service annuity shall be provided for widows of present employees. A widow's service annuity shall be provided for widows of future entrants and present employees.
A retirement annuity shall consist of a service annuity and a prior service annuity where applicable, and a widow's annuity shall consist of a widow's service annuity and a widow's prior service annuity, where applicable.
If the total annuities to an employee from accumulation for prior service annuity and service annuity, or to a widow for widow's service annuity and widow's prior service annuity, as an actuarial equivalent of such accumulations, effective on or after July 1, 1983 are less than $100 per month, a temporary annuity of $100 per month shall be payable to the employee or widow, except in the case of a reciprocal pension.
Except as to a temporary annuity, the annuity payable to an employee or widow shall consist of equal monthly payments for life or widowhood, provided that upon termination thereof due to death or other cause, payment shall be made for the period from the date of the last payment to the date of termination. The first payment of any annuity shall be due and payable 1 month after the occurrence of the event upon which payment thereof depends; provided, that as to annuities effective July 1, 1973, and thereafter payments shall be made as of the first day of each calendar month during the annuity payment period, the first payment to be made as of the first day of the calendar month coincidental with or next following the first day of the annuity payment period and the last payment to be made as of the first day of the calendar month in which the annuitant dies or the annuity payment period ends.
40 ILCS 5/12-128