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Jefferson County, Colorado facts for kids

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Jefferson County
Jefferson County Courthouse in Golden
Jefferson County Courthouse in Golden
Gateway to the Rocky Mountains
Map of Colorado highlighting Jefferson 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 Thomas Jefferson
Seat Golden
Largest city Lakewood
 • Total 774 sq mi (2,000 km2)
 • Land 764 sq mi (1,980 km2)
 • Water 9.8 sq mi (25 km2)  1.3%%
 • Estimate 
 • Density 763/sq mi (295/km2)
Time zone UTC−7 (Mountain)
 • Summer (DST) UTC−6 (MDT)
Congressional districts 1st, 2nd, 7th

Jefferson County is a county located in the U.S. state of Colorado. As of the 2020 census, the population was 582,910, making it the fourth-most populous county in Colorado. The county seat is Golden, and the most populous city is Lakewood.

Jefferson County is included in the Denver-Aurora-Lakewood, CO Metropolitan Statistical Area. Located along the Front Range of the Rocky Mountains, Jefferson County is adjacent to the state capital of Denver.

In 2010, the center of population of Colorado was located in Jefferson County.

The county's slogan is the "Gateway to the Rocky Mountains", and it is commonly nicknamed Jeffco. The name Jeffco is incorporated in the name of the Jeffco School District, the Jeffco Business Center Metropolitan District No. 1, and several businesses located in Jefferson County. Jeffco is also incorporated in the unofficial monikers of many Jefferson County agencies. The Rocky Mountain Metropolitan Airport operated by Jefferson County was previously known as the Jeffco Airport.

A major employer in Jefferson County is the large Coors Brewing Company in Golden. Also, the state-supported Colorado School of Mines is located in Jefferson County, focusing on topics such as mining, geology, chemistry, and engineering.


On August 25, 1855, the Kansas Territorial Legislature created Arapahoe County to govern the entire western portion of the territory. The county was named for the Arapaho Nation of Native Americans that lived in the region.

In June 22, 1850, gold was discovered along the South Platte River in Arapahoe County (in present-day Englewood). This discovery precipitated the Pike's Peak Gold Rush. Many residents of the mining region felt disconnected from the remote territorial governments of Kansas and Nebraska, so they voted to form their own Territory of Jefferson on October 24, 1859. The following month, the Jefferson Territorial Legislature organized 12 counties for the new territory, including Jefferson County. Jefferson County was named for the namesake of the Jefferson Territory, Thomas Jefferson, the principal author of the Declaration of Independence and the nation's third president. Golden City served as the county seat of Jefferson County. Robert Williamson Steele, Governor of the Provisional Government of the Territory of Jefferson from 1859 to 1861, built his home in the county at Mount Vernon and later at Apex.

The Jefferson Territory never received federal sanction, but during his last week in office, President James Buchanan signed an act which organized the Territory of Colorado on February 28, 1861. That November 1, the new Colorado General Assembly organized the 17 original counties of Colorado, including a new Jefferson County. In 1908, the southern tip of Jefferson County was transferred to Park County, reducing Jefferson County to its present length of 54 miles (87 km). Several annexations by the City & County of Denver and the 2001 consolidation of the City & County of Broomfield removed the east and extreme northwestern portion of the county, respectively.


According to the U.S. Census Bureau, the county has a total area of 774 square miles (2,000 km2), of which 764 square miles (1,980 km2) is land and 9.8 square miles (25 km2) (1.3%) is water.

Adjacent counties

Jefferson County is one of the few counties in the United States to border as many as ten counties.

Recreational areas

  • Alderfer/Three Sisters Park
  • Apex Park
  • Bear Creek Lake Park
  • Centennial Cone Park
  • Clear Creek Canyon Park
  • Coal Creek Canyon
  • Crown Hill Park
  • Deer Creek Canyon Park
  • Elk Meadow Park
  • Fairmount Trail
  • Flying J Ranch Park
  • Hildebrand Ranch Park
  • Hiwan Homestead Museum
  • Lair o' the Bear Park
  • Lewis Meadows Park
  • Lookout Mountain Nature Center
  • Matthews/Winters Park
  • Meyer Ranch Park
  • Mount Falcon Park
  • Mount Galbraith Park
  • Mount Glennon
  • Mount Lindo
  • North Table Mountain Park
  • Pine Valley Ranch Park
  • Ranson/Edwards Homestead Ranch
  • Reynolds Park
  • Sister City Park
  • South Table Mountain Park
  • South Valley Park
  • Standley Lake Regional Park
  • Van Bibber Park
  • Welchester Tree Grant Park
  • White Ranch Park
  • Windy Saddle Park
  • Urban Trails

Major highways

  • U.S. Highway 6
  • U.S. Highway 40
  • U.S. Highway 285
  • Interstate 70
  • State Highway 93
  • State Highway 470


Historical population
Census Pop.
1870 2,390
1880 6,804 184.7%
1890 8,450 24.2%
1900 9,306 10.1%
1910 14,231 52.9%
1920 14,400 1.2%
1930 21,810 51.5%
1940 30,725 40.9%
1950 55,687 81.2%
1960 127,520 129.0%
1970 233,031 82.7%
1980 371,753 59.5%
1990 438,430 17.9%
2000 527,056 20.2%
2010 534,543 1.4%
2020 582,910 9.0%
U.S. Decennial Census

1790-1960 1900-1990

1990-2000 2010-2020

As of the census of 2000, there were 527,056 people, 206,067 households, and 140,537 families residing in the county. The population density was 683 people per square mile (264 people/km²). There were 212,488 housing units at an average density of 275 people per square mile (106 people/km²). The racial makeup of the county was

Black or African American
Native American
Pacific Islander
from other races
9.95% of the population were either Hispanic or Latino of any race
2.18% in two or more races

There were 206,067 households, out of which 33.40% had children under age 18 living with them, 55.10% were married couples living together, 9.10% had a female householder with no husband present, and 31.80% were non-families. 24.50% of all households were made up of individuals, of those 6.30% were someone living alone who was 65 years of age or older. The average household size was 2.52, and the average family size was 3.03 persons.

In the county, the population ages were spread out:

under age 18
aged 18–24
from 25–44
from 45–64
65 years of age or older
The median age was 37 years.

For every 100 females there were 99.00 males. For every 100 females age 18 and over, there were 96.80 males.

The median income for a household in the county was $57,339, and the median income for a family was $67,310. Males had a median income of $45,306 versus $32,372 for females. The per capita income for the county was $28,066. About 3.40% of families and 5.20% of the population were below the poverty line, including 5.80% of those under age 18, and 5.10% of those age 65 or over.

According to a report in the JAMA, residents of Jefferson County had a 2014 life expectancy of 80.02 years.


State parks

National forests and wilderness

National wildlife refuges

Historic trail

  • South Platte Trail

Recreational trails

Scenic byway

Golf courses

  • Applewood Golf Course
  • Bear Creek Golf Club
  • Evergreen Golf Course
  • Foothills Golf Course
  • Fossil Trace Golf Course
  • Fox Hollow Golf Course
  • Heritage Golf Course at Westmoor
  • Hiwan Golf Club
  • Homestead Golf Course
  • Indian Tree Golf Club
  • Lake Arbor Golf Course
  • Lakewood Country Club
  • Racoon Creek Golf Course
  • Rolling Hills Country Club




Census-designated places

Unincorporated communities


  • Jefferson County School District R-1.

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