40 ILCS 5/2-110.1
An active participant having no creditable service as a participating employee under Article 7 of this Code may establish service credit in this system for periods during which the participant held an elective office in a county, township or municipality, (including the full term for which elected if he or she resigned such office to enter the armed forces of the United States), provided the member cannot establish service credit under Article 7 for such periods because the county, township or municipality did not and does not subscribe to coverage for that office under that Article. Credit for such service may be established in this system by the participant paying to this system an amount equal to (1) the contribution rate in effect for participants at the date of membership in this system multiplied by the salary then in effect for the members of the General Assembly for each year of service for which credit is allowed, plus (2) the State's share of the normal cost of benefits under this system expressed as a percent of payroll, as determined by the system's actuary as of the date of the participant's membership in this system multiplied by the salary then in effect for members of the General Assembly, for each year of service for which credit is allowed, plus (3) interest on (1) and (2) above at 4% per annum compounded annually from the date of membership to the date of payment by the participant.
However, if application for such credit is made between January 1, 1992 and April 1, 1992, the applicant need not pay the amount indicated in item (2) above, but only the sum of items (1) and (3).
40 ILCS 5/2-110.1