35 ILCS 200/9-105

The books for the assessment of property, in counties not under township organization, shall be made up by congressional townships, but parts or fractional townships may be added to full townships, at the discretion of the county board. In counties under township organization, the books shall be made to correspond with the organized townships. Separate books shall be made for the assessment of property and the collection of all taxes and special assessments thereon, within the corporate limits of cities, incorporated towns and villages, if ordered by the county board.