Thurston County was created out of Lewis County by the government of Oregon Territory on January 12, 1852. At that time, it covered all of the Puget Sound region and the Olympic Peninsula. On December 22 of the same year, Pierce, King, Island, and Jefferson Counties were split off from Thurston County.
At the 2000 census, there were 207,355 people, 81,625 households and 54,933 families residing in the county. The population density was 285 per square mile (110/km²). There were 86,652 housing units at an average density of 119 per square mile (46/km²). The racial makeup of the county was 85.66% White, 2.35% Black or African American, 1.52% Native American, 4.41% Asian, 0.52% Pacific Islander, 1.69% from other races, and 3.85% from two or more races. 4.53% of the population were Hispanic or Latino of any race. 17.1% were of German, 10.2% English, 9.8% Irish, 6.9% United States or American and 5.5% Norwegian ancestry according to Census 2000.
There were 81,625 households of which 33.00% had children under the age of 18 living with them, 53.10% were married couples living together, 10.30% had a female householder with no husband present, and 32.70% were non-families. 25.10% of all households were made up of individuals and 8.00% had someone living alone who was 65 years of age or older. The average household size was 2.50 and the average family size was 2.99.
Age distribution was 25.30% under the age of 18, 9.30% from 18 to 24, 29.30% from 25 to 44, 24.60% from 45 to 64, and 11.40% who were 65 years of age or older. The median age was 36 years. For every 100 females there were 96.00 males. For every 100 females age 18 and over, there were 92.70 males.
The median household income was $46,975, and the median family income was $55,027. Males had a median income of $40,521 versus $30,368 for females. The per capita income for the county was $22,415. About 5.80% of families and 8.80% of the population were below the poverty line, including 9.80% of those under age 18 and 5.00% of those age 65 or over.