35 ILCS 250/25

The corporate authorities of a county to which this Act applies may use any county record or other information that predates the effective date of this Act by up to 5 years for the purpose of determining whether an increase in the market value of a longtime owner-occupant's principal residence is a consequence of the refurbishing or renovating of other residences or the construction of new residences in long-established residential areas or areas of deteriorated, vacant, or abandoned homes and properties.