Mich. Comp. Laws § 418.151: Employers subject to act.

Sec. 151.

The following constitutes employers subject to this act:

The state; each county, city, township, incorporated village, and school district; each incorporated public board or public commission in this state authorized by law to hold property and to sue or be sued generally; and any library in a county with a population less than 600,000 established under Act No. 138 of the Public Acts of 1917, being sections 397.301 to 397.305 of the Michigan Compiled Laws, if the library board by resolution expresses its intention to be considered as a separate employer from the county where it is located for purposes of this act.

Every person, firm, limited liability company, limited liability partnership, and private corporation, including any public service corporation, who has any person in service under any contract of hire, express or implied, oral or written, unless those employees excluded according to the provisions of section 161(5) comprise all of the employees of the person, firm, limited liability company, limited liability partnership, or corporation.