From the Guide to 2010 Census State and Local Geography — Washington, History:

The United States acquired the area of Washington through a treaty with Great Britain in 1846. Washington Territory was organized from part of Oregon Territory on March 2, 1853; it included all of present-day Washington, northern Idaho, and northwestern Montana. In 1859, when Oregon was admitted as a state, the remainder of Oregon Territory, the rest of Idaho, additional area of Montana, and part of Wyoming was added to Washington Territory. Washington Territory assumed generally the same boundary as the present state when Idaho Territory was organized in 1863. Washington was admitted to the Union on November 11, 1889, as the 42nd state.

Although the territory had not yet been legally established, census data for Washington are available beginning with the 1850 census. The 1850 and 1860 populations are for the entire territory as legally established in 1859, when it included all of Idaho and part of Montana and Wyoming. The population of the entire legally established Oregon Territory (of which the area of Washington was a part) in 1850 was 13,294.

Data for the legally established state of Washington are available beginning with the 1890 census.

From QuickFacts: statistics for all states and counties, and for cities and towns with a population of 5,000 or more.

Note: The dashboard shown above is cropped at the bottom. Click on the image to see the full dashboard. Click here to see the table view showing the United States, Washington, Seattle city, Spokane city, Tacoma city, and Olympia city (state capital)

Sources: 2018 Population Estimates; 2013-2017 American Community Survey, 5-Year Estimates; 2010 Census. Community Facts — Find popular facts (population, income, etc.) and frequently requested data about your community.

Source: 2018 Population Estimates.

Source: 2018 American Community Survey, 1-Year Estimates.

From the Statistics in Schools program:

From Census Business Builder: Regional Analyst Edition - 2.6:

From the State Data Center (SDC) Program:

From Foreign Trade > U.S. International Trade Data:

Note: After you create an account, select options for State Export Data (Origin of Movement) or State Import Data (State of Destination) by HS or NAICS. Select State (Washington) and Measures, Commodity, Country and/or Time for data. For more information, see Quick Start Guide.

Sources: 2014 Population Estimates and 2014 American Community Survey, 1-Year Estimates.

Sources: 2009-2013 American Community Survey, 5-Year Estimates, 2012 Survey of Business Owners and other federal data.

Source: 2012 Economic Census. The U.S. Census Bureau will release 2017 Economic Census statistics from September 2019 through 2021.

From the Guide to 2010 Census State and Local Census Geography: