Fort Ridgely was a frontier United States Army outpost from 1851 to 1867, built 1853–1854 in Minnesota Territory. The Sioux called it Esa Tonka. It was located overlooking the Minnesota River southwest of Fairfax, Minnesota. Half of the fort's land was part of the south reservation in the Minnesota river valley for the Mdewakanton and Wahpekute tribes. Fort Ridgely had no defensive wall, palisade, or guard towers. The Army referred to the fort as the "New Post on the Upper Minnesota" until it was named for two Maryland Army Officers named Ridgely, who died during the Mexican–American War.