35 ILCS 200/9-225
Resolutions of any county board dividing the county into four assessment districts, if adopted before January 1, 1990, shall remain valid thereafter unless and until repealed by the county board.
The county board of any county may, by resolution adopted after January 1, 1992, divide the county into 4 assessment districts. The county clerk shall forward a copy of the resolution to the Department. The assessment districts shall follow township lines if the county is organized into townships, and shall divide, as near as may be, the work of assessing the property in the county into 4 equal parts. Neither the area nor the number of parcels of property need be equal in the 4 assessment districts. The resolution shall number the assessment districts 1 to 4 inclusive. The general assessment years for assessment district number 1 shall be 1992 and every fourth year thereafter; for assessment district number 2, the general assessment years shall be 1993 and every fourth year thereafter; for assessment district number 3, the general assessment years shall be 1994 and every fourth year thereafter; and for assessment district number 4, the general assessment years shall be 1995 and every fourth year thereafter. However, the general assessments shall not include property constituting a farm which is assessed under Sections 10-110 through 10-140. The county board of any county divided into assessment districts under this paragraph may provide by resolution for the assessment of the entire county in the general assessment year provided by law for that county and for the dissolution of the assessment district after the first such assessment.
35 ILCS 200/9-225