40 ILCS 5/8-230
An employee may contribute to the fund for all periods of service (including periods served in the armed forces of the United States if he left the service of the employer to enter the armed forces and returned to the service of the employer within 180 days after his discharge from the armed service, and if the employer has not made such payment on his behalf) except for those periods for which he received credit in another annuity and benefit fund or pension fund in operation in the city for the benefit of employees of the employer, rendered by him to the employer after the effective date by virtue of appointment or election to a position not covered by the provisions of this Article, such amounts as he would have contributed for annuity purposes had deductions from his salary been made for the purposes of the fund, at the rates in effect and in accordance with the provisions relating to future entrants and present employees during the period such service was rendered. Upon making such payments, he shall be credited with concurrent city contributions at the rates in effect during the time such service was rendered. Such payments and concurrent city contributions shall be made with interest at the effective rate and shall, together with all other amounts contributed by or for such employee, be considered in computing the annuities for him and his widow, and any such service for which payment is made shall be counted as service under this Article.
Until the effective date of this amendatory Act of 1991, in order that the foregoing service may be counted for the purposes of Section 8-138, payment must be made in full while the employee is in service; if payment in full is not made, any payments made on account shall be refunded to him when he withdraws from service, or paid to his widow if he is dead. If there is no widow, a refund shall be paid as provided in this Article, with interest at the effective rate. An employee, however, may elect to have such partial payments, together with the concurrent city contributions and interest, credited and applied for age and service and widow's annuity, for himself and his wife, on the assumption that the payments made shall apply beginning with his earliest service, or his widow, if the employee dies in service, may elect to have such amounts credited for widow's annuity purposes, to the extent that they do not increase her annuity above that which she could have received if her proportionate part of the payments and related city contributions were included and considered, and an annuity were fixed for her on the assumption her deceased husband had continued in service at the rate of his final salary until he became age 65.
Beginning on the effective date of this amendatory Act of 1991, an employee who is still in service may elect to establish credit under this Section for only a fraction of the service that he or she is eligible to establish under this Section. In such cases, the credit established shall be deemed to relate to the earliest service for which credit may be established, and shall be counted for the purposes of Section 8-138. However, in no event shall such credit be granted until the corresponding employee contributions have been paid.
Beginning on the effective date of this amendatory Act of 1997, any employee who is in service, or within 90 days after withdrawing from service, or who is an active contributor to a participating system as defined in the Retirement Systems Reciprocal Act, may make payments and establish credit under this Section.
40 ILCS 5/8-230