40 ILCS 5/12-120

"Employer": Any board of park commissioners referred to in this Article and the retirement board defined in this Article. Effective January 1, 1959, "employer" shall also include any city to which is transferred by virtue of the "Exchange of Functions Act of 1957" the employment of employees of a park district (other than park policemen) who are members of the fund established by "The 1919 Act".