40 ILCS 5/15-113.7
"Service for other public employment": Includes those periods not exceeding the lesser of 10 years or 2/3 of the service granted under other Sections of this Article dealing with service credit, during which a person was employed full time by the United States government, or by the government of a state, or by a political subdivision of a state, or by an agency or instrumentality of any of the foregoing, if the person (1) cannot qualify for a retirement pension or other benefit based upon employer contributions from another retirement system, exclusive of federal social security, based in whole or in part upon this employment, and (2) pays the lesser of (A) an amount equal to 8% of his or her annual basic compensation on the date of becoming a participating employee subsequent to this service multiplied by the number of years of such service, together with compound interest from the date participation begins to the date payment is received by the board at the rate of 6% per annum through August 31, 1982, and at the effective rates after that date, and (B) 50% of the actuarial value of the increase in the retirement annuity provided by this service, and (3) contributes for at least 5 years subsequent to this employment to one or more of the following systems: the State Universities Retirement System, the Teachers' Retirement System of the State of Illinois, and the Public School Teachers' Pension and Retirement Fund of Chicago. If a function of a governmental unit as defined by Section 20-107 is transferred by law, in whole or in part to an employer, and an employee transfers employment from this governmental unit to such employer within 6 months of the transfer of the function, the payment for service authorized under this Section shall not exceed the amount which would have been payable for this service to the retirement system covering the governmental unit from which the function was transferred.
The service granted under this Section shall not be considered in determining whether the person has the minimum of 8 years of service required to qualify for a retirement annuity at age 55 or the 5 years of service required to qualify for a retirement annuity at age 62, as provided in Section 15-135. The maximum allowable service of 10 years for this governmental employment shall be reduced by the service credit which is validated under paragraph (2) of subsection (b) of Section 16-127 and paragraph one of Section 17-133.
Except as hereinafter provided, this Section shall not apply to persons who become participants in the system after September 1, 1974.
40 ILCS 5/15-113.7