Mich. Comp. Laws § 252.3
When any 2 or more adjoining counties combine under the terms of this act, they shall establish an inter-county highway commission which shall be composed of the state highway commissioner or his deputy, and 6 members from each of the counties participating, as follows: the 3 county road commissioners, the chairman of the county board of supervisors, and 2 members selected by the board of supervisors who shall be members thereof: Provided, however, That if a roads and bridges committee has been established by said county board of supervisors, the chairman of such committee shall be 1 of the 2 members thus selected: Provided further, That if a regional planning commission, created under the provisions of Act No. 281 of the Public Acts of 1945, as amended, being sections 125.11 to 125.23, inclusive, of the Compiled Laws of 1948, has been or shall be formed in any of the counties participating hereunder, the director of such regional planning commission shall be an ex officio member of the inter-county highway commission.
MCL 252.3