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Boulder County, Colorado facts for kids

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Boulder County
Boulder County Courthouse
Boulder County Courthouse
Official seal of Boulder County
Map of Colorado highlighting Boulder County
Location within the U.S. state of Colorado
Map of the United States highlighting Colorado
Colorado's location within the U.S.
Country  United States
State  Colorado
Founded November 1, 1861
Named for large granite boulders in area
Seat Boulder
Largest city Boulder
 • Total 740 sq mi (1,900 km2)
 • Land 726 sq mi (1,880 km2)
 • Water 14 sq mi (40 km2)  1.9%%
 • Estimate 
 • Density 460/sq mi (176/km2)
Time zone UTC−7 (Mountain)
 • Summer (DST) UTC−6 (MDT)
Congressional districts 2nd, 4th

Boulder County is a county located in the U.S. state of Colorado of the United States. As of the 2020 census, the population was 330,758. The most populous municipality in the county and the county seat is Boulder.

Boulder County comprises the Boulder, CO Metropolitan Statistical Area, which is included in the DenverAurora, CO Combined Statistical Area.


Boulder County was one of the original 17 counties created by the Territory of Colorado on November 1, 1861. The county was named for Boulder City and Boulder Creek, so named because of the abundance of boulders in the area. Boulder County retains essentially the same borders as in 1861, although a 27.5 square miles (71.2 km2) of its southeastern corner and its approximate population of 40,000 became part of the City and County of Broomfield in 2001.


Boulder Pano from Fairview HS
Boulder and the mountains to the west of the city

According to the U.S. Census Bureau, the county has a total area of 740 square miles (1,900 km2), of which 726 square miles (1,880 km2) is land and 14 square miles (36 km2) (1.9%) is water.

Adjacent counties

National protected areas

  • Arapaho National Forest
  • Roosevelt National Forest
  • Indian Peaks Wilderness
  • James Peak Wilderness

Rocky Mountain National Park is in Boulder County, Larimer County, and Grand County. Longs Peak, the park's highest summit at 4,345 meters (14,255 feet) elevation, is located in Boulder County.

State protected area

Scenic trails and byways

  • Continental Divide National Scenic Trail
  • Peak to Peak Scenic and Historic Byway

Historic district


Historical population
Census Pop.
1870 1,939
1880 9,723 401.4%
1890 14,082 44.8%
1900 21,544 53.0%
1910 30,330 40.8%
1920 31,861 5.0%
1930 32,456 1.9%
1940 37,438 15.4%
1950 48,296 29.0%
1960 74,254 53.7%
1970 131,889 77.6%
1980 189,625 43.8%
1990 226,374 19.4%
2000 271,651 20.0%
2010 294,567 8.4%
2020 330,758 12.3%
U.S. Decennial Census
1790-1960 1900-1990
1990-2000 2010-2020

As of the census of 2000, there were 271,651 people, 114,680 households, and 68,808 families residing in the county. The population density was 392 people per square mile (151/km2). There were 119,900 housing units at an average density of 162 per square mile (62/km2). The racial makeup of the county was 88.54% White, 0.88% Black or African American, 0.61% Native American, 3.06% Asian, 0.06% Pacific Islander, 4.67% from other races, and 2.18% from two or more races. 10.46% of the population were Hispanic or Latino of any race.

There were 114,680 households, out of which 30.70% had children under the age of 18 living with them, 48.90% were married couples living together, 7.70% had a female householder with no husband present, and 40.00% were non-families. 26.30% of all households were made up of individuals, and 5.50% had someone living alone who was 65 years of age or older. The average household size was 2.47 and the average family size was 3.03.

In the county, the population was spread out, with 22.90% under the age of 18, 13.40% from 18 to 24, 33.60% from 25 to 44, 22.30% from 45 to 64, and 7.80% who were 65 years of age or older. The median age was 33 years. For every 100 females, there were 102.20 males. For every 100 females age 18 and over, there were 101.70 males.

In 2014, the median income for a household in the county was $69,407, and the median income for a family was $94,938. Males had a median income of $65,489 versus $48,140 for females. About 7.0% of families and 14.6% of the population were below the poverty line, including 14.6% of those under age 18 and 5.9% of those age 65 or over.

In 2017, Bloomberg ranked the Boulder metropolitan area as the top "brain" area in the US.


Map of Boulder County, Colorado
Boulder County, Colorado



Census-designated places

Other unincorporated communities

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