40 ILCS 5/5-170
Beginning on the effective date 1%, and beginning January 1, 1976, 1-1/2% of the salary of each male present employee and future entrant shall be deducted and contributed to the fund for widow's annuity or Tier 2 surviving spouse's annuity; however, in the case of a future entrant who attains age 63 prior to January 1, 1988 while still in service, no deductions shall be made for the period between the date the employee attains age 63 and January 1, 1988. The deductions shall be made from each payment of salary and shall continue during the employee's service.
An employee in the service and over age 57 on the effective date of this amendatory Act of 1969 shall have the option of contributing 1% of salary together with the effective rate of interest for service rendered by him subsequent to his attainment of age 57 and prior to such effective date. If such retroactive contributions are made the wife or widow shall be entitled to the widow's annuity provided in Section 5-136.
Concurrently with each such deduction, the city shall contribute 2% of each such payment of salary.
Each deduction from salary and contribution by the city shall be allocated to the account of and credited to the employee. The amount so credited shall be improved at the applicable rate of interest; except that in the case of an employee who attains age 63 prior to January 1, 1988 while still in service, no interest shall be credited between the date the employee attains age 63 and January 1, 1988.
40 ILCS 5/5-170