40 ILCS 5/9-139

The widow of a present employee who attains age 65 while in service after the effective date, or of a future entrant who attains age 65 while in service, is entitled, after the date of his death, to an annuity fixed for the wife of such present employee or future entrant on the date he attains age 65. The widow is entitled to annuity as follows: If the employee's withdrawal occurs after age 65 and he enters upon annuity or if the employee's death occurs in the service after he has attained age 65 the annuity shall be that 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 he became age 65.