David Thompson was one of North America’s greatest pathfinders. He explored and documented vast reaches of North America, some believe as much as a fifth of the continent. Thompson was the first American man to explore the Columbia River Basin as well as the Kootenai, Pend Oreille, and Clark Fork river basins. He surveyed most of the shore of Lake Superior; and established the first fur posts the first posts west of the continental divide, in Idaho, Oregon and western Montana and. He also wrote the first ethnography of northern plain Indians.
Thompson preceded Lewis and Clark by many years and his effort s to describe the relationship of the Missouri River to the rivers of central Canada, helped direct Lewis and Clark on their trek. He crossed and re-crossed the trans-Mississippi west and establishing new water trails, at a time when anything west of the Great Lakes was considered wilderness.
Thompson was born to Welsh parents in London in 1770. As a child, he attended charity school and later apprenticed to the Hudson Bay Company. He documented the longitude and latitude of North West Company post that might be affected by the Jay Treaty of 1797 which attempted to set the U.S. Canadian border and limit British influence on American soil. This survey placed the origin of the Mississippi well south of the Lake of the Woods and was crucial in promoting the 49th parallel as the international boundary across the plains.
From 1817 to1827 Thompson surveyed the international border between the U.S. and Canada from Quebec to the Lake of the Woods.