55 ILCS 5/5-1110

Every county board which issues building or occupancy permits shall forward a copy of the building or occupancy permit to the township assessor and a copy to the county assessor, supervisor of assessments or board of assessors, as the case may be, 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 application the index number.