Cassopolis is a village in the U.S. state of Michigan. As of the 2000 census, the village population was 1,740. It is the county seat of Cass County. 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.