65 ILCS 5/9-4-1

Property not within the corporate limits but contiguous to any local improvement made by a municipality pursuant to the provisions of this Article may be charged by the corporate authorities of the municipality in an amount not greater than the benefit conferred by the local improvement on such property. This Division 4 shall apply only to municipalities of less than 500,000 inhabitants and shall not be exercised with respect to any contiguous property where such property is included within the corporate limits of another municipality.