35 ILCS 200/9-5
Each county assessor, board of appeals, and board of review shall make and publish reasonable rules for the guidance of persons doing business with them and for the orderly dispatch of business.
In counties with fewer than 3,000,000 inhabitants, these rules shall not require specific proof to be offered nor limit the nature of evidence which may be offered as a condition of filing an assessment complaint under Section 16-55.
In counties with 3,000,000 or more inhabitants, the county assessor and board of appeals (ending the first Monday in December 1998 and the board of review beginning the first Monday in December 1998 and thereafter), jointly shall make and prescribe rules for the assessment of property and the preparation of the assessment books by the township assessors in their respective townships and for the return of those books to the county assessor.
35 ILCS 200/9-5