70 ILCS 1837/15

All property of every kind owned by the District shall be exempt from taxation. However, a tax may be levied upon a lessee of the District by reason of the value of a leasehold estate separate and apart from the fee simple title or upon any improvements that are constructed and owned by others than the District. All property of the District shall be public grounds owned by a municipal corporation and used exclusively for public purposes within the tax exemption provisions of Sections 15-10, 15-15, 15-20, 15-30, 15-75, 15-140, 15-155, and 15-160 of the Property Tax Code.