40.09°N 105.36°W / 40.09; -105.36

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Boulder County
County
Boulder County Courthouse
Seal
Location within the U.S. state of Colorado
Colorado's location within the U.S.
Coordinates: 40°05′N 105°22′W
Country	United States
State	Colorado
Founded	November 1, 1861
Named for	large granite boulders in area
Seat	Boulder
Largest city	Boulder
Area
• Total	740 sq mi (1,900 km2)
• Land	726 sq mi (1,880 km2)
• Water	14 sq mi (40 km2)  1.9%
Population  (2020)
• Total	330,758[1]
• Density	460/sq mi (176/km2)
Time zone	UTC−7 (Mountain)
• Summer (DST)	UTC−6 (MDT)
Congressional districts	2nd, 4th
Website	www.bouldercounty.org

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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.^[1] The most populous municipality in the county and the county seat is Boulder.^[2]

Boulder County comprises the Boulder, Colorado Metropolitan Statistical Area, which is included in the Denver–Aurora, Colorado Combined Statistical Area.^[3]

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 creek which hampered early gold prospecting efforts. 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.

Before the arrival of the first US settlers, the area was occupied by Native Americans led by Chief Niwot on the plains and seasonally by Utes in the mountains to the west. The first European American settlers were gold prospectors led by Captain Thomas Aikins. His group of about twenty settled at the mouth of Boulder Creek Canyon on October 17, 1858. Chief Niwot told them not to stay and it is said they promised to move into the mountains to prospect in the spring. However, in February 1859, they founded the town of Boulder. At about the same time, they also founded the first Gold Mining town in what would become Colorado, Gold Hill which is about 10 miles west from Boulder. Gold Hill was founded because of the placer gold discovered there. The area was the site of the first commercial scale placer mine in Colorado, producing over 5,500 ounces of gold in the first year of operations (1859).^[4]

In late December 2021, the Marshall Fire raged through the parched lands near Boulder, Colorado. Marshall Fire is the most destructive in Colorado's history.^[5] The fire impacted City of Superior, City of Louisville and unincorporated Boulder County areas. 991 homes were destroyed with an additional 127 damaged. Over 13,000 people in Superior and 21,000 in Louisville were ultimately evacuated while the fire was spreading due to unusual 100 mile per hour winds. Additionally, one person died and another is missing and presumed dead.^[6] The cause of the fire has not been officially announced, pending an investigation.^[7] However, an incident report filed by a ranger with Boulder Open Space and Mountain Parks identified two ignition points for the fire. The first ignition point was a shed that began to burn at approximately 11:30AM MST, December 30, 2021. The second ignition point was upwind from the first, and started around noon of the same day on "western side of the Marshall Mesa trailhead".^[8][9][10]

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.^[11]

As of the census^[17] 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 people/km²). There were 119,900 housing units at an average density of 162 per square mile (63/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.^[18] 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.^[19]

Boulder County is divided into three districts each represented by a commissioner elected county-wide. The three commissioners comprise the county Board of Commissioners and represent the county as a whole. Each commissioner must reside in their respective district and may be elected to a maximum of two four-year terms.

The Board of County Commissioners are full-time public servants and approve the budget for the entire County government. The Board also oversees the management of 10 County departments and the daily operations of the county, work that is done by a county manager or a chief administrative officer in some counties.

Boulder County has seven other county-wide elected officials, including the District Attorney, who represents the 20th Judicial District.^[20]

Boulder County went Republican in all but three presidential elections from 1920 to 1984, the exceptions being the national Democratic landslides of 1932, 1936 and 1964. However, it has swung heavily to the Democrats since the late 1980s, and has supported Democrats at every election since 1988. Since the 1990s, it has become one of the most liberal counties in Colorado; in most years, it is the second-strongest Democratic bastion in the state, behind only the City and County of Denver. The GOP has not crossed the 40% mark in the county since 1988. This tracks closely with the Democratic trend in other counties dominated by college towns.

In recent years, the GOP has turned in some of its worst showings in the county in memory. Republicans took less than 28% of the vote in Boulder County in both 2008 and 2012, only 22% in 2016, and just over 20% in 2020.

In 2000, Green Party presidential candidate Ralph Nader took 11.82% of the vote in Boulder County, more than twice the 5.25% he took statewide in Colorado, and more than four times his 2.73% nationwide vote share.^[23]

Boulder County has also demonstrated its progressive leanings in referendums on social issues, such as in 2006, when nearly 2/3 of Boulder County voters voted to reject Amendment 43, a constitutional amendment defining marriage as between one man and one woman. Although the amendment passed statewide with 55% of the vote, only 33% of Boulder County supported it.^[25] In 2012, over 66% of Boulder County voted in favor of Amendment 64, legalizing marijuana in the state of Colorado.

The 20th Judicial District of Colorado, the state trial court of general jurisdiction, serves and is coextensive with Boulder County. As of 2009 the 20th Judicial Circuit has eight District Court judges. The Boulder County Court, the state trial court of limited jurisdiction, consists of five judges and six magistrates.

Boulder County has two combined courthouses:

• The Boulder County Justice Center is located in the City of Boulder and is headquarters to the 20th Judicial District of Colorado. The office of the district attorney is also here, as is the Juvenile Assessment Center, the county's combined assessment and detention facility.
• The Longmont Courthouse in the City of Longmont acts as an extension of the County Court and the District Attorney's Office.^[26]

School districts serving Boulder County include:^[27]

• Boulder Valley School District RE-2
• Estes Park School District R-3
• St. Vrain Valley School District RE-1J
• Thompson School District R-2J

• Bibliography of Colorado
• Geography of Colorado
  • Marfell Lakes
• History of Colorado
  • 2013 Colorado floods
  • Jackson County, Jefferson Territory
  • National Register of Historic Places listings in Boulder County, Colorado
• Index of Colorado-related articles
• List of Colorado-related lists
  • List of counties in Colorado
  • List of statistical areas in Colorado
• Outline of Colorado
  • Front Range Urban Corridor