620 ILCS 50/46
One Commissioner shall hold office for one year, two shall hold office for two years, and two shall hold office for three years from the First day of July following their election, but each until his successor is elected and qualified.
Annually thereafter the county board shall at its first session of its regular meeting held in the month of June of each year, elect as before, the number of Commissioners whose terms expire on July 1st and who shall hold office for three years and until their successors are elected and qualified.
Vacancies on the Commission, occasioned by removal, resignation or otherwise shall be reported to the county clerk, who shall so notify the county board and shall be filled in like manner as original appointments.
620 ILCS 50/46