Only white males over 21 who had resided in the Territory for six months and were citizens or had declared their intention to become naturalized citizens could vote.
The future Washington Territory (later state) was part of Oregon Territory until March 2, 1853, when U.S. President Millard Fillmore signed a bill creating Washington Territory. Oregon Territory conducted a census in 1849 and counted 304 residents living north of the Columbia River (the area of the future Washington). In 1850, the U.S. Census counted 1,049 settlers in north Oregon. The population was located along the Columbia River concentrated at Fort Vancouver, along the Cowlitz River, at the head of Budd Inlet (the future site of Olympia), and near Fort Nisqually.
At the time of the census, Washington Territory had eight counties. Following is a list of the counties, giving total settler population and number of eligible voters (white males over 21).
- Clarke County population 1,134, voters 466
- Thurston County population 996, voters 381
- Lewis County population 616, voters 239
- Pierce County population 513, voters 276
- Island County population 195, voters 80
- Jefferson County population 189, voters 68
- King County population 170, voters 111
- Pacific County population 152, voters 61