U.S. Route 287 runs through town, following the Madison River as it descends from West Yellowstone. The town is flanked by Tobacco Root Mountains to the northwest, the Gravelly Range to the southwest and the Madison Range to the east. Approximately north of town, the Madison Dam creates Ennis Lake at the head of Bear Trap Canyon. A large "E" has been placed in a hill west of the town at this location:
Ennis is served by the Big Sky Airport.
Prior to the arrival of Europeans, the Shoshone, Flathead, and Bannock tribes hunted the Madison Valley each spring. The Lewis and Clark Expedition viewed the Madison Valley in July 1805 from Three Forks, prior to ascending the Jefferson. It can be assumed that some of their party came through Ennis on their journey.
In 1863, gold was discovered in Alder Gulch. This brought on "the rush." Two months later, William Ennis homesteaded the site along the Madison River that was soon to become the town of Ennis, his namesake.
In 1886 a mystery creature was noted for making livestock kills in the Madison Valley. A local rancher Israel Ammon Hutchins finally shot & killed the beast, after accidentally shooting one of his cattle, which was on the other side of some brush. A local taxidermist stuffed the canine. Jack Kirby (Hutchins' Grandson) tracked the mount to a Museum in Pocatello, Idaho, around 2007. The "critter" was to be displayed at the Madison Valley History Association in Ennis, but in August 2008 the Association only had photos & documents posted in its windows.
Avid Aircraft, a manufacturer of homebuilt aircraft, was located in Ennis. The company ceased operations in 2003.