615 ILCS 65/5
The City of Chicago may use for any of the purposes conferred and authorized by Division 123 of Article 11 of the "Illinois Municipal Code", approved May 29, 1961, as now or hereafter amended, may sell and convey, or may lease for any term of years, any part or parts or all of the lands granted to the City by this Act for industrial, manufacturing or harbor purposes. When any lands are sold or leased, such grant or lease shall contain a clause in the deed, or lease to the effect that the lands shall be used for the purpose authorized within a certain time fixed or agreed upon between the City of Chicago and its grantees or lessees.
Before any such sale or lease shall become effective, such sale or lease shall be approved in writing by the Director of Natural Resources and, in case of approval, there shall be affixed to the instrument by which such sale or lease is effective, the seal of the Department of Natural Resources. The approval, or the refusal to approve of such sale or lease, shall be made by the Director within 30 days from the date of filing such application, and in case the Director does not act on the application within 30 days from the date of the filing of such application, by approving or disapproving same in writing, the sale or lease shall be deemed to have been approved and the same shall take effect accordingly without the seal of the Department being affixed.
615 ILCS 65/5