This was part of the territory of the Omaha people. Explored in 1805 by the Lewis and Clark expedition following the Louisiana Purchase of 1803 by the United States, this area was settled by European-American fur traders, adventurers, farmers, and finally entrepreneurs. All initially depended on the Missouri River as a main transportation corridor and source of water. Sarpy County has served as the springboard for Nebraska's settlement and expansion. The county is named for Colonel Peter Sarpy, an early fur trader at Fontenelle's Post in the Bellevue area in the 1840s. He also had Sarpy's post in what became Decatur; Sarpy died in Plattsmouth in 1865.