Calvin Township, Cassopolis, MI - Home Calvin Township is a civil township of Cass County in the U.S. state of Michigan. The population was 2,041 at the 2000 census.According to the United States Census Bureau, the township has a total area of 35.6 square miles of which, 34.4 square miles of it Calvintownship.com~Site InfoWhoisTrace RouteRBL Check