High Quality Content by WIKIPEDIA articles! Fort Assinniboine, a fort in Montana and within the military Department of Dakota, was built in 1879, in the aftermath of the Great Sioux War of 1876-77 and the disastrous defeat of U.S. Army forces led by General Custer at the Battle of Little Big Horn on June 25, 1876. The fort is located in Hill County six miles southwest of Havre (the county seat) on Highway 87. The fort gets its name from the Assinniboine people.