Ennis is a town in Madison County, Montana, United States, in the southwestern part of the state. The population was 840 at the 2000 census. The elevation of Ennis is 4,941 feet (1,506 m) above sea level. U.S. Route 287 runs through town, following the Madison River as it descends from West Yellowstone. Just downstream from town is Ennis Lake, formed by the Madison Dam.