Engineer Cantonment is an archaeological site in Washington County, in the state of Nebraska in the Midwestern United States. Located in the floodplain of the Missouri River near present-day Omaha, Nebraska, it was the temporary winter camp of the scientific party of the Yellowstone Expedition. From October 1819 to June 1820, the party studied the geology and biology of the vicinity, and met with the local indigenous peoples. Their eight-month study of the biota has been described as "the first biodiversity inventory undertaken in the United States".

The Yellowstone expedition was an expedition to the American frontier in 1819 and 1820 authorized by United States Secretary of War John C. Calhoun, with the goal of establishing a military fort or outpost at the mouth of the Yellowstone River in present-day North Dakota. Sometimes called the Atkinson–Long Expedition after its two principal leaders, Colonel Henry Atkinson and Major Stephen Harriman Long, it led to the creation of Fort Atkinson in present-day Nebraska, the first United States Army post established west of the Missouri River, but was otherwise a costly failure, stalling near Council Bluffs, Iowa.