Otsego is a city in Allegan County in the U.S. state of Michigan. The population was 3,956 at the 2010 census. The city is within Otsego Township, but is administratively autonomous. Otsego is situated on M-89 about three miles (5 km) west of Plainwell and US 131. It is about nine miles (14 km) southeast of Allegan and the Kalamazoo River flows east to west through the city.