40 ILCS 5/15-144
This Section applies only to the death benefits of persons who became participants before August 22, 1997 (the effective date of Public Act 90-511).
If a deceased participant has specified in a written notice on file with the board prior to his or her death, or if the participant has not so specified, but the beneficiary specifies in the application for the death benefit that the benefit be paid as an annuity or as a designated cash payment plus an annuity, it shall be paid in the manner thus specified, unless the annuity is less than $10 per month, in which case the death benefit shall be paid in a single cash sum. If the death benefit is paid as an annuity, the beneficiary may elect to take an amount not in excess of $500 in a single cash sum. The annuity payable to a beneficiary shall be the actuarial equivalent of the death benefit, determined as of the participant's date of death, on the basis of the age of the beneficiary at that time.
The beneficiary annuity payment period shall begin on the day following the death of the deceased and shall terminate on the date of the beneficiary's death. If the beneficiary may receive the death benefit in a single cash sum, but elects to receive an annuity, he or she may, within one year after the death of the participant or annuitant, revoke this election and receive in a single cash sum the excess of the amount of the death benefit upon which the annuity was based over the sum of the annuity payments received.
40 ILCS 5/15-144