35 ILCS 200/10-223

Beginning with the 1992 assessment year, the equalized assessed value of any tract of real property that has not been used as a farm for 20 or more consecutive years shall not be determined under Sections 10-110 through 10-140. If no other use is established, the tract shall be considered to be used for open space purposes and its valuation shall be determined under Sections 10-155 through 10-165.