Cassopolis is a village in the U.S. state of Michigan and the county seat of Cass County. It is located mostly in LaGrange Township with a small portion extending east into Penn Township. The village and county are named after statesman Lewis Cass, a New Hampshire native and a prominent U.S. senator from Michigan prior to the American Civil War. Cassopolis is part of the South Bend–Mishawaka, IN-MI, Metropolitan Statistical Area sometimes referred to as Michiana.