Eaton Rapids is a city in Eaton County in the U.S. state of Michigan. The population was 5,214 at the 2010 census. The city is located in the s…Eaton Rapids is a city in Eaton County in the U.S. state of Michigan. The population was 5,214 at the 2010 census. The city is located in the south of Eaton Rapids Township, on the boundary with Hamlin Township, though it is politically independent of both townships. Its nickname is the Island City, since the downtown is located on an island, with a public park, in the Grand River.