65 ILCS 5/11-39-1

Every municipality in counties containing 200,000 or more inhabitants which issues building permits shall forward a copy of the building permit to the township assessor and a copy to the county assessor of the county in which the municipality is situated within 15 days of issuance of the permit. The permit shall show the complete legal description of the area to which the permit pertains; and, if the area has a "property index number", as defined and referred to in Section 9-45 of the Property Tax Code, then there shall be included in the permit the index number.