40 ILCS 5/8-145

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