On February 8, 1853 a bill was introduced in congress to make the portion of the Oregon Territory north of the Columbia River (and the 46th parallel east of the Columbia) the Washington Territory. At the time this area included all of present day Washington state, plus northern Idaho and a chunk of Montana.
Originally the area was to be called it the Columbia Territory, but Washington won out. The current capital, Olympia, was also the capital of the territory.
Map credit: Map by Matthew Trump, used under Creative Commons Attribution ShareAlike 3.0 license.