Fort Pierre is a city in Stanley County, South Dakota, United States. It is part of the Pierre, South Dakota micropolitan area and the county seat of Stanley County. The population was 2,078 at the 2010 census.
The settlement of Fort Pierre developed around an 1832 trading post and fort situated on the west bank of the Missouri River, near the confluence with its tributary Bad River. But another American-owned trading post had been operating nearby since 1817, and in 2017 the city celebrated its bicentennial of continuous permanent settlement.
On March 30, 1743, Francois and Louis-Joseph Gaultier de La Vérendrye reached the area of present-day Fort Pierre during an expedition west from Quebec, a French colony in present-day Canada. They left a lead plate buried in a hill to claim the land for the King of France. In the 1803 Louisiana Purchase, the United States acquired this area and the remainder of France's vast territory west of the Mississippi River.
President Thomas Jefferson commissioned the Lewis and Clark Corps of Discovery Expedition in 1804 to explore the territory, especially by traveling west to the Upper Missouri and Platte rivers, in the hope of finding a water route to the Pacific Ocean. They met with the Teton Sioux on the south side of the mouth of the Bad River on 24–28 September 1804.