Mich. Comp. Laws § 780.160

Sec. 10. (1) Jurisdiction of any proceeding in this state under this act is vested in the circuit court. (2) The proper venue if this state is acting as an initiating state is in the county in which the petitioner resides or in which a valid prior and existing support order has been issued. The proper venue if this state is acting as a responding state and a valid support order has been issued in this state is in the county in which the support order was issued. The proper venue if this state is acting as a responding state and a valid support order has not been issued in this state is in the county in which the obligor resides or is found.