Section 40 ILCS 5/2-117 - Participants - Election not to participate(a) Every person who was a member on November 1, 1947, or in military service on such date, is subject to the provisions of this system beginning upon such date, unless prior to such date he or she filed with the board a written notice of election not to participate. Every person who becomes a member after November 1, 1947, and who is then not a participant becomes a participant beginning upon the date of becoming a member unless, within 24 months from that date, he or she has filed with the board a written notice of election not to participate.
(b) A member who has filed notice of an election not to participate (and a former member who has not yet begun to receive a retirement annuity under this Article) may become a participant with respect to the period for which the member elected not to participate upon filing with the board, before April 1, 1993, a written rescission of the election not to participate. Upon contributing an amount equal to the contributions he or she would have made as a participant from November 1, 1947, or the date of becoming a member, whichever is later, to the date of becoming a participant, with interest at the rate of 4% per annum until the contributions are paid, the participant shall receive credit for service as a member prior to the date of the rescission, both before and after November 1, 1947. The required contributions shall be made before commencement of the retirement annuity; otherwise no credit for service prior to the date of participation shall be granted.