Which U.S. expedition first reached the Pacific Ocean overland from the eastern United States in 1805?

The Lewis and Clark Expedition first reached the Pacific Ocean overland from the eastern United States in 1805.

President Thomas Jefferson commissioned the expedition after the 1803 Louisiana Purchase. The Corps of Discovery left Camp Dubois near St. Louis on May 14, 1804, under the command of Meriwether Lewis and William Clark. Its mission included mapping the newly acquired territory, studying its natural resources, and seeking a practical route across the continent.

The party crossed the Rocky Mountains near Lemhi Pass and followed rivers westward to the Columbia River. It sighted the Pacific Ocean on November 7, 1805, and spent the winter at Fort Clatsop near present-day Astoria, Oregon. The expedition returned to St. Louis on September 23, 1806.

Sacagawea traveled with the expedition and helped with communication and local knowledge, while York, an enslaved member of Clark’s household, also participated. The expedition did not discover an all-water route across the continent, but it produced maps and information that expanded U.S. knowledge of the West.