Washington is a city in Tazewell County, Illinois, United States. Washington is on U.S. Route 24 and Illinois Route 8, northeast of East Peoria. The population was 15,134 at the 2010 census, a 39.6 percent increase over 2000.
Washington is located at 40°42′N 89°25′W / 40.700°N 89.417°W / 40.700; -89.417 (40.7039, -89.4206). According to the 2010 census, Washington has a total area of 8.182 square miles (21.19 km), of which 8.17 square miles (21.16 km) (or 99.85%) is land and 0.012 square miles (0.03 km) (or 0.15%) is water.
As of the census of 2000, there were 10,841 people, 4,189 households, and 3,091 families residing in the city. The population density was 1,450.0 people per square mile (559.6/km²). There were 4,403 housing units at an average density of 588.9 per square mile (227.3/km²). The racial makeup of the city was 98.36% White, 0.26% African American, 0.08% Native American, 0.42% Asian, 0.26% from other races, and 0.62% from two or more races. Hispanic or Latino of any race were 0.67% of the population.
There were 4,189 households out of which 35.3% had children under the age of 18 living with them, 63.8% were married couples living together, 7.7% had a female householder with no husband present, and 26.2% were non-families. 22.5% of all households were made up of individuals and 8.5% had someone living alone who was 65 years of age or older. The average household size was 2.56 and the average family size was 3.02.
In the city, the population was spread out with 26.0% under the age of 18, 7.9% from 18 to 24, 29.7% from 25 to 44, 23.3% from 45 to 64, and 13.0% who were 65 years of age or older. The median age was 37 years. For every 100 females, there were 95.3 males. For every 100 females age 18 and over, there were 90.5 males.
The median income for a household in the city was $71,702, and the median income for a family was $61,184. Males had a median income of $64,388 versus $43,460 for females. The per capita income for the city was $24,231. About 2.8% of families and 4.1% of the population were below the poverty line, including 4.5% of those under age 18 and 3.5% of those age 65 or over.