The Lewis and Clark Expedition began its journey across the United States in 1804.
President Thomas Jefferson commissioned the expedition soon after the Louisiana Purchase. Its official purpose was to explore the newly acquired territory, find a practical route to the Pacific Ocean, study geography and natural resources, and establish relations with Native nations.
Meriwether Lewis and William Clark led the Corps of Discovery. The expedition departed from Camp Dubois near present-day Hartford, Illinois, in May 1804, traveled up the Missouri River, crossed the Rocky Mountains, and reached the Pacific coast in November 1805.
The explorers returned to St. Louis in September 1806. Their maps and reports expanded American knowledge of the continent, although the expedition entered lands already inhabited and governed by numerous Indigenous peoples.