50 ILCS 105/1
No member of a county board, during the term of office for which he or she is elected, may be appointed to, accept, or hold any office other than (i) chairman of the county board or member of the regional planning commission by appointment or election of the board of which he or she is a member, (ii) alderperson of a city or member of the board of trustees of a village or incorporated town if the city, village, or incorporated town has fewer than 1,000 inhabitants and is located in a county having fewer than 50,000 inhabitants, or (iii) trustee of a forest preserve district created under Section 18.5 of the Conservation District Act, unless he or she first resigns from the office of county board member or unless the holding of another office is authorized by law. Any such prohibited appointment or election is void. This Section shall not preclude a member of the county board from being appointed or selected to serve as (i) a member of a County Extension Board as provided in Section 7 of the County Cooperative Extension Law, (ii) a member of an Emergency Telephone System Board as provided in Section 15.4 of the Emergency Telephone System Act, (iii) a member of the board of review as provided in Section 6-30 of the Property Tax Code, or (iv) a public administrator or public guardian as provided in Section 13-1 of the Probate Act of 1975. Nothing in this Act shall be construed to prohibit an elected county official from holding elected office in another unit of local government so long as there is no contractual relationship between the county and the other unit of local government. This amendatory Act of 1995 is declarative of existing law and is not a new enactment.
50 ILCS 105/1