55 ILCS 5/2-3002.5
Beginning with members elected at the general election in 2002, counties having a population between 800,000 and 3,000,000 according to 2000 decennial census shall have no more than 18 members on their county board. If the chairman of the county board is elected at-large by the voters of the county as provided in Section 2-3007, the chairman shall not be counted as a member of the county board for the purpose of the limitations on the size of the county board provided in this Section. Neither a member nor the chairman of that county board shall serve simultaneously as commissioner or president of the board of commissioners of the forest preserve district. No person shall seek election to both the county board and the forest preserve commission at the same election.
55 ILCS 5/2-3002.5