Arapahoe County (/əˈræpəhoʊ/ ə-RAP-ə-hoh) is one of the 64 counties in the U.S. state of Colorado. As of the 2010 census, the population was 572,003, making it the third-most populous county in Colorado. The county seat is Littleton, and the most populous city is Aurora. The county was named for the Arapaho Native American tribe who once lived in the region.
According to the U.S. Census Bureau, the county has a total area of 805 square miles (2,080 km), of which 798 square miles (2,070 km) is land and 7.3 square miles (19 km) (0.9%) is water. The county measures 72 miles (116 kilometers) east to west and 4 to 12 miles (6 to 19 kilometers) south to north.
Two exclaves of Arapahoe County are entirely surrounded by the City and County of Denver, the City of Glendale and the Holly Hills neighborhood, a census-designated place.
As of the census of 2000, there were 487,967 people, 190,909 households, and 125,809 families residing in the county. The population density was 608 people per square mile (235/km²). There were 196,835 housing units at an average density of 245 per square mile (95/km²). The racial makeup of the county was 79.93% White, 7.67% Black or African American, 0.66% Native American, 3.95% Asian, 0.12% Pacific Islander, 4.51% from other races, and 3.16% from two or more races. 11.81% of the population were Hispanic or Latino of any race.
There were 190,909 households out of which 34.90% had children under the age of 18 living with them, 51.20% were married couples living together, 10.60% had a female householder with no husband present, and 34.10% were non-families. 27.00% of all households were made up of individuals and 5.90% had someone living alone who was 65 years of age or older. The average household size was 2.53 and the average family size was 3.11.
In the county, the population was spread out with 26.70% under the age of 18, 8.60% from 18 to 24, 33.10% from 25 to 44, 23.00% from 45 to 64, and 8.60% who were 65 years of age or older. The median age was 34 years. For every 100 females there were 97.10 males. For every 100 females age 18 and over, there were 94.20 males.
The median income for a household in the county was $53,570, and the median income for a family was $63,875. Males had a median income of $41,601 versus $31,612 for females. The per capita income for the county was $28,147. About 4.20% of families and 5.80% of the population were below the poverty line, including 7.00% of those under age 18 and 5.10% of those age 65 or over.
Arapahoe County was once a Republican stronghold, and a classic bastion of suburban conservatism. However, like many other suburban counties around the country, the margin gradually declined in the 1990s and early 2000s, reflecting the county’s growing and more diverse population. In 2008, the county swung over dramatically to support Barack Obama, who became the first Democrat to carry it since 1964, and only the second since 1944. Four years earlier, George W. Bush had won the county by four points; in 2008, Obama won it by 13 points. It voted for Obama by a similar margin in 2012, and provided much of Hillary Clinton’s statewide margin in 2016.