40 ILCS 5/9-119
"Annuity": Equal monthly payments for life, unless otherwise specified. The first payment shall be due and payable 1 month after the occurrence of the event upon which payment of the annuity depends, and the last payment shall be payable as of the date of the annuitant's death and be prorated from the date of the last preceding payment to the date of death; 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 5/9-119