40 ILCS 5/8-110

"Employer": (1) a city of more than 500,000 inhabitants; (2) the Board of Education of the city, with respect to any of its employees who participate in this Fund; (3) the Chicago Housing Authority, with respect to any of its employees who participate in this Fund subject to the provisions of Section 8-230.9; (4) the Public Building Commission of the city, with respect to any of its employees who participate in this Fund; and (5) the Retirement Board.