| Oregon Territory The Territory of Oregon was an organized incorporated territory of the United States that existed from August 14, 1848, until February 14, 1859, when the southwestern portion of the territory was admitted to the Union as the State of Oregon. Originally claimed by several countries (See Oregon Country), the region was divided between the U.S. and Great Britain in 1846. When established, the territory encompassed an area that included the current states of Oregon, Washington, and Idaho, as well as parts of Wyoming and Montana. The capital of the territory was first Oregon City, then Salem, followed briefly by Corvallis, and lastly as Salem, the seat of government for the State of Oregon. |