High Quality Content by WIKIPEDIA articles! The Territory of Washington was an organized incorporated territory of the United States that existed from February 8, 1853, until November 11, 1889, when the final extent of the territory was admitted to the Union as the State of Washington.The Washington Territory was created from the portion of the Oregon Territory north of the lower Columbia River and north of the 46th parallel east of the Columbia; that had been ceded by Britain in the 1846 Oregon Treaty as settlement of the Oregon Boundary Dispute.