Mich. Comp. Laws § 455.310

Sec. 10. All lands acquired by any corporation organized under this act or subject to its control and management shall be held in trust as aforesaid for public parks, playgrounds, boulevards and pleasure drives for the recreation, health, welfare and benefit of the public and shall be free to all persons, subject to such necessary and reasonable rules and regulations as shall, from time to time, be adopted for the well-ordering and government thereof. And all such lands and personal property so held in trust for such purposes shall be exempt from taxation.