70 ILCS 1810/3.1

All property of every kind belonging to the Illinois International Port District shall be exempt from taxation, provided that 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, or upon such improvements as are constructed and owned by others than the Port District. All property of the Illinois International Port District shall be construed as constituting public grounds owned by a municipal corporation and used exclusively for public purposes within the tax exemption provisions of Section 15-155 of the Property Tax Code.