Black River is a 78.8-mile-long (126.8 km) river in the U.S. state of Michigan, flowing mostly northward through four Northern Michigan counties: Otsego, Montmorency, Presque Isle, and Cheboygan. The Black River flows into the Cheboygan River at (45°36′13″N84°27′47″W), just south of the city of Cheboygan, and then into Lake Huron. The main branch of the Black River rises in Charlton Township in east-central Otsego County near the boundary with Montmorency County. The East Branch of the Black River rises less than a mile to the east in Vienna Township in Montmorency County.