40 ILCS 5/9-141

The widow of an employee who attains age 60 or more but less than age 65 while in service and who withdraws from service shall be entitled after his death, to an annuity fixed on the date of withdrawal. The annuity shall be the amount provided on a reversionary annuity basis from the total sum accumulated to his credit for widow's annuity and (if he was a present employee) widow's prior service annuity as of the date of withdrawal.