Mich. Comp. Laws § 500.5006

Sec. 5006. (1) Any number of persons, not less than 7, may associate together and form a stock insurer to transact any or all of the following kinds of insurance: Property, marine, inland navigation and transportation, or automobile insurance (limited), all as defined in chapter 6. (2) Thirteen or more persons may organize a stock insurer for the purpose of transacting any of the following kinds of insurance: Life, disability, casualty, or fidelity and surety, all as defined in chapter 6 or title as defined in chapter 73. (3) Any number of persons, not less than 20, a majority of whom shall be citizens of this state, may become together with others who may hereafter be associated with them or their successors, a body corporate for the purpose of transacting life insurance, or life and disability insurance, on the mutual plan. (4) Any number of persons, not less than 13, may incorporate a stock insurer for the purpose of insuring railway employees against loss of position, for transacting disability and life insurance, and granting annuities, all as identified in section 6604.