Interest on sums accumulated to the credit of such employee shall be adjusted for the periods of time during which such contributions are made.
Upon making such contributions he shall be credited with concurrent county contributions at the rates in effect for county employees during the periods such service was rendered. Such payments and concurrent county contributions shall be made with interest at the effective rate and shall, together with all other amounts contributed by such employee for annuity purposes, be considered in computing the annuities to which such employee or his widow shall have a right. Any such periods of service for which payment is made shall be counted as periods of service for annuity purposes.
In order to be credited as service under Section 9--134 of this Article all such payments by a county employee must be made in full while the employee is still in service of the county. If payment is not so made any payments made with interest at the effective rate shall be refunded to the employee when he withdraws from service, or to his widow in the event of his death, or if no widow, in accordance with the other refund provisions of this Article. The employee may elect to have such partial payments made by him, together with the concurrent county contributions and interest, credited toward the age and service and widow's annuities on the assumption that the payments shall apply to his earliest service. In the event of death of the employee, while in service, his widow may elect to have such payments and related county contributions, and interest, credited for widow's annuity, to the extent that they do not increase her annuity above that fixed for her on the assumption her deceased husband had continued in service at the rate of his final salary until he became 65 years of age, and the proportional part of the payments and related contributions were included.
40 ILCS 5/9-179