Mich. Comp. Laws § 117.24

Sec. 24. If the charter, or any amendment thereto, whether of cities incorporated under the provisions of this act, or under an existing charter of the city heretofore granted or passed by the legislature for the government of the city, be approved, then 2 printed copies thereof, with the vote for and against duly certified by the city clerk shall, within 30 days after the vote is taken, be filed with the secretary of state, and a like number with the county clerk of the county in which such city is located and shall thereupon become law, unless a different date for the taking effect of such charter or charter amendment, or any part thereof, is specifically set forth therein.