70 ILCS 1831/15

All property of every kind owned by the Port District shall be exempt from taxation. However, 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 such improvements as are constructed and owned by others 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.