75 ILCS 65/3a
The corporate authorities of any park district whose limits are co-extensive with the limits of any city, village, or incorporated town lying wholly within any congressional township, in which there is established and maintained a free public library under "The Illinois Local Library Law", approved July 12, 1965, as heretofore or hereafter amended, or the corporate authorities of any such city, village, or incorporated town having the control or supervision of any public park or parks, may permit the board of library trustees having control of such library or the board of trustees of a library district whose geographical area of service includes all or part of a public park or park district to erect and maintain in any public park of such park district, city, village, or incorporated town, a library building which shall be under the exclusive control and supervision of the board of library trustees, so long as such building is used as a free public library; and may contract with such board of library trustees relative to the erection and maintenance and administration thereof. Any portion of such building less than the whole which shall not from time to time be needed for library purposes, may be rented for public purposes only by the board of library trustees to or with the consent of such park district, city, village, or incorporated town.
75 ILCS 65/3a