The Oregon Country was a predominantly American term referring to a disputed region of the Pacific Northwest of North America. The region was occupied by British and French Canadian fur traders from before 1810, and American settlers from the mid-1830s, with its coastal areas north from the Columbia River frequented by ships from all nations engaged in the maritime fur trade, most of these from the 1790s through 1810s being Boston-based. The Oregon Treaty of 1846 ended disputed joint occupancy pursuant to the Treaty of 1818 and established the British-American boundary at the 49th parallel (except Vancouver Island).
Oregon was a distinctly American term for the region. The British used the term Columbia District instead. The Oregon Country consisted of the land north of 42°N latitude, south of 54°40′N latitude, and west of the Rocky Mountains—with the eastern border generally running on or close to the Continental Divide—westwards to the Pacific Ocean. The area now forms part of the present day Canadian province of British Columbia, all of the US states of Oregon, Washington, and Idaho, and parts of Montana and Wyoming. The British presence in the region was generally administered by the Hudson's Bay Company, whose Columbia Department comprised most of the Oregon Country and extended considerably north into New Caledonia and beyond 54°40′N, with operations reaching tributaries of the Yukon River.
George Vancouver explored Puget Sound in 1792. Vancouver claimed it for Great Britain on 4 June 1792, naming it for one of his officers, Lieutenant Peter Puget. Alexander Mackenzie was the first European to cross North America by land north of New Spain. arriving at Bella Coola on what is now the Central Coast of British Columbia in 1793. From 1805 to 1806 Meriwether Lewis and William Clark explored the territory for the United States on the Lewis and Clark Expedition. David Thompson, working for the Montreal-based North West Company, explored much of the region beginning in 1807, with his friend and colleague Simon Fraser following the Fraser River to its mouth in 1808, attempting to ascertain whether or not it was the Columbia, as had been theorized about it in its northern reaches through New Caledonia, where it was known by its Dakleh name as the "Tacoutche Tesse". Thompson was the first European to voyage down the entire length of Columbia River. Along the way, his party camped at the junction with the Snake River on July 9, 1811. He erected a pole and a notice claiming the country for Great Britain and stating the intention of the North West Company to build a trading post on the site. Later in 1811, on the same expedition, he finished his survey of the entire Columbia, arriving at a partially constructed Fort Astoria two months after the departure of John Jacob Astor's ill-fated Tonquin.