70 ILCS 1801/15

All property of every kind owned by the Port District shall be exempt from taxation, provided that a tax may be levied upon a lessee of the Port 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 persons other than the Port District. All property of the Port 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.