40 ILCS 5/11-141

The widow of an employee who, (1) attains age 55 or more but less than age 60 in service, and (2) has served 10 or more years and (3) withdraws from service, shall be entitled after his death to an annuity fixed as of the date of withdrawal. The widow is entitled to receive the amount provided on a reversionary annuity basis from the total sum accumulated to the employee's credit on the date when the annuity was fixed, as follows: (1) If service is 20 or more years, the total credits for widow's annuity and in addition, if he was a present employee, the total credits for widow's prior service annuity; or (2) If service is 10 or more but less than 20 years, the total credits for widow's annuity from employee contributions and 1/10 of the total credits for widow's annuity from city contributions for each year of service after the first 10 years, including for the widow of a present employee 1/10 of the total credits for widow's prior service annuity from city contributions for each year of service after the first 10 years.