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.
Fort Assinniboine was established primarily to ward off possible attacks by the Sioux, led by Chief Sitting Bull, from the Cypress Hills and by the Nez Perce, some of whom were also in Canada following the defeat and capture of Chief Joseph by the U.S. Army in the Battle of Bear Paw in 1877. However, no such attack or raid ever occurred.
The fort was located on a massive reserve and, at its peak, housed over 750 officers, enlisted men, and their families. With 104 buildings, the fort remains one of the largest ever built in the United States. Among the military officers stationed at the fort in the 1890s was John Pershing, who later achieved fame as the leader of the American Expeditionary Force in World War I.
In 1916, a portion of Fort Assinniboine was ceded to the Rocky Boy Indian Reservation (home of the Chippewa Cree tribe).
Another portion of the reserve was ceded to Hill County to create Beaver Creek Park, the largest county park in the United States. Most of the buildings at the Fort were razed; a handful of surviving structures are now an agricultural extension station associated with Montana State University.