Ashton is situated in the farmland at the northeast end of the Snake River Plain. The nearly level terrain of the plain extends for miles to the south and west. To the north lies the Henry’s Fork Caldera, a ancient volcanic crater. Its rim rises a thousand feet above Ashton, and its slopes are covered in forests. The Teton Mountains are visible on the horizon to the east.
In 1900, the Union Pacific Railroad wanted to extend its St. Anthony Railroad up to West Yellowstone to capture market share on tourists visiting Yellowstone National Park. They proposed a line passing through Marysville and past Warm River and into the Henry’s Fork Caldera, and across Rea’s Pass. But the residents of Marysville did not want a railroad passing through their land. So a new town was founded just west of Marysville. It was named after Bill Ashton, an engineer for the Oregon Short Line (a subsidiary of Union Pacific). Marysville quickly dwindled and Ashton quickly grew. It was incorporated in 1906.
Two rivers pass by Ashton. The Henry’s Fork River flows westward along the bottom of the Henry’s Fork Caldera and then bends southward to pass Ashton on the west. The Ashton Reservoir was created by a dam on the Henry’s Fork straight west from Ashton. The Falls River has its source in Yellowstone National Park to the east, and flows by Ashton on the south side. The two rivers meet to the southwest.
The climate at Ashton is unusually moist compared to much of Idaho, with 20 inches of rain falling annually, with even more falling in the higher elevations to the north and east.
Ashton's population was 1,129 as of the 2000 census. The elevation is 5,259 feet. Large numbers of people pass through Ashton on U.S. Highway 20 in the summer, visiting Yellowstone, as well as the Island Park area. To the south it leads to important Idaho towns including Rexburg and Idaho Falls. State Highway 47 begins at Ashton and heads west and then north to pass the scenic Mesa Falls. State Highway 32 heads south from Ashton.