  the territory of washington was an organized incorporated territory of the united states that existed from march 2, 1853, until november 11, 1889, when the territory was admitted to the union as the state of washington. it 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. at its largest extent, it also included the entirety of modern idaho and parts of montana and wyoming, before attaining its final boundaries in 1863. ==history==  agitation in favor of self-government developed in the regions of the oregon territory north of the columbia river in 1851â1852. a group of prominent settlers from the cowlitz and puget sound regions met on november 25, 1852, at the "monticello convention", to draft a petition to the united states congress calling for a separate territory north of the columbia river. after gaining approval from the oregon territorial government, the proposal was sent to the federal government.{{cite web | title = settlers met at monticello to sign a petition asking congress to create a separate territory north of the columbia river | work = washington history | publisher = washington secretary of state | url = http://www.sos.wa.gov/history/timeline/detail.aspx?id=214 | accessda
History_of_Washington_(state) History_of_the_American_West Pre-statehood_history_of_Washington_(state) States_and_territories_disestablished_in_1889 States_and_territories_established_in_1853 Washington_Territory