40 ILCS 5/11-124
"Annuity": Equal monthly payments for life, unless terminated earlier under Section 11-148, 11-152, 11-153, or 11-230.
For annuities taking effect before January 1, 1998, the first payment shall be due and payable one month after the occurrence of theevent upon which payment of the annuity depends. Until August 1, 1999, payment shall be made for any part of a monthly period in which death of the annuitant occurs. Beginning August 1, 1999, all payments shall be made on the first day of the calendar month and shall be for the entire calendar month, without proration. The last payment shall be made onthe first day of the calendar month in which the annuity payment period ends. A pro rata amount shall be paid for that part of the month from the July 1999 annuity payment date through July 31, 1999.
For annuities taking effect on or after January 1, 1998, payments shall be made as of the first day of the calendar month, with 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 annuity payment period ends.
For annuities taking effect on or after January 1, 1998, all payments shall be for the entire calendar month, without proration.
For the purposes of this Section, the "annuity payment period" means the period beginning on the day after the occurrence of the event upon which payment of the annuity depends, and ending on the day upon which the death of the annuitant or other event terminating the annuity occurs.
40 ILCS 5/11-124