The Yellowstone Expedition was a frontier expedition authorized in 1818 by United States Secretary of War John C. Calhoun to establish a military fort or outpost near present-day Bismarck, North Dakota at the mouth of the Yellowstone River.

Sometimes called the Atkinson-Long Expedition, it leads to the creation of Fort Atkinson (Nebraska), the first United States Army post to be established west of the Missouri River, but is otherwise a costly failure, stalling near Council Bluffs, Iowa.