Washington County is in eastern Nebraska on the Missouri River. It was explored by Europeans as early as 1739 by Pierre Antoine and Paul Mallet, who were on a trapping expedition to Canada. In 1804, Lewis and Clark reported the establishment of the new United States government to a council of Indian chiefs near the present site of Fort Calhoun. As a result of this Council, Fort Atkinson was established in 1819 and served as a key midwestern outpost until 1827.