60 ILCS 1/25-15

When township organization ceases in any county as provided in this Article, the county board may by ordinance or resolution restructure into a commission form of government on or before 180 days after a township organization ceases. If the county board votes to assume a commission form of government, an election shall be held in the county at the next general election in an even-numbered year for 3 county commissioners who shall hold office for 2, 4, and 6 years, respectively, and until their successors are elected and qualified. Terms shall be determined by lot. At each succeeding general election after the first, one commissioner shall be elected.