40 ILCS 5/16-166

Each trustee, prior to assuming office, shall take and subscribe to an oath that he or she will diligently and honestly administer the affairs of the board, and that he or she will not knowingly violate or willingly permit to be violated any of the provisions of law applicable to the retirement system. The oath shall be certified by the officer before whom it is taken, and immediately filed in the office of the Secretary of State.