Mich. Comp. Laws § 125.1606

Sec. 6. Not more than 1 corporation shall be organized under this act for a municipality, except for subsidiaries established pursuant to section 6a. If a corporation is organized at the county level, thereafter, a corporation may be organized for a municipality within that county, the effect of which shall be to exclude that municipality from subsequent project jurisdiction of the county corporation, except on specific subsequent consent by the governing body of the municipality. The organization of a corporation at less than the county level does not preclude the organization of a corporation at the county level for the remainder of the county. More than 1 corporation may join or cooperate in a project or act together in coordinating more than 1 project.