Mich. Comp. Laws § 124.454

Sec. 4. (1) A political subdivision or a combination of 2 or more political subdivisions may form a public authority under this act. A county with a population between 240,000 and 255,000 may form more than 1 public authority under this act. A city, village, township, or county forming a public authority by itself or in combination with 1 or more other political subdivisions may provide that only a portion of the city, village, township, or county shall become part of the public authority. The portion of the city, village, township, or county to become part of the public authority shall be bounded by precinct lines drawn for election purposes. (2) Formation of a public authority pursuant to subsection (1) shall be accomplished by adoption of articles of incorporation by an affirmative vote of a majority of the members elected to and serving on the legislative body of each political subdivision.