Jefferson County
U.S. county
Jefferson County Courthouse in Golden
Motto:  Gateway to the Rocky Mountains
Location within the U.S. state of Colorado
Colorado's location within the U.S.
Coordinates: 39°35′N 105°15′W / 39.59°N 105.25°W / 39.59; -105.25
Country	United States
State	Colorado
Founded	November 1, 1861
Named for	Thomas Jefferson
Seat	Golden
Largest city	Lakewood
Area
• Total	774 sq mi (2,000 km2)
• Land	764 sq mi (1,980 km2)
• Water	9.8 sq mi (25 km2)  1.3%
Population
• Estimate  (2020)	582,910
• Density	763/sq mi (295/km2)
Time zone	UTC−7 (Mountain)
• Summer (DST)	UTC−6 (MDT)
Congressional districts	1st, 2nd, 6th, 7th
Website	www.jeffco.us

Jefferson County is a county located in the U.S. state of Colorado. As of the 2020 census, the population was 582,910,^[1] making it the fourth-most populous county in Colorado. The county seat is Golden,^[2] 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.^[3]

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, a university specializing in mining, geology, chemistry, and engineering is located in Jefferson County.

History

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 who lived in the region.

On June 22, 1858, 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.^[4] 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.^[5] 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 northeastern corner of the county, respectively.

Geography

Long Scraggy Peak in the southeastern part of the county.

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.^[6]

Adjacent counties

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

Major highways

• 
  Interstate 70
• I-70 BS
• 
  U.S. Highway 6
• 
  U.S. Highway 40
• 
  U.S. Highway 285
• 
  State Highway 8
• 
  State Highway 58
• 
  State Highway 72
• 
  State Highway 74
• 
  State Highway 75
• 
  State Highway 93
• 
  State Highway 121
• 
  State Highway 391
• 
  State Highway 470
• Chatfield Ave
• 44th Ave

Recreational areas

Demographics

As of the census^[11] 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

90.59%		White
0.89%		Black or African American
0.75%		Native American
2.28%		Asian
0.08%		Pacific Islander
3.23%		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:

25.30%		under age 18
8.10%		aged 18–24
32.10%		aged 25–44
24.90%		aged 45–64
9.60%		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.^[12]

Education

The sole school district serving the county is Jefferson County School District R-1.^[13]

Private schools

• Colorado Academy

Tertiary institutions

• Colorado Christian University
• Colorado School of Trades

Jefferson County Public Library is the county library system.

Government and infrastructure

• The Federal Correctional Institution, Englewood is in unincorporated Jefferson County.^[14]
• The Rocky Flats Plant produced nuclear weapons in Jefferson County from 1952 until 1989.
• The Jefferson County Public Library, established in 1952.
• The Jefferson County Government Center, also known as the "Taj Mahal".
• The Denver Federal Center, the largest concentration of federal government agencies outside of Washington, D.C., is located in Lakewood.

Sheriff's office

The Jefferson County Sheriff's Office responded to the 1999 Columbine High School massacre, and investigated it together with the F.B.I. The Sheriff's Office received backlash after it was revealed the agency had the perpetrators Eric Harris and Dylan Klebold in and out of custody prior to the shooting. After the shooting Sue Klebold sued the Sheriff's office for failing to prevent their son from carrying out the Columbine High shootings. According to a "notice of intent to sue" filed by Susan and Thomas Klebold, county officials were "reckless, willful and wanton" in the way they handled a 1998 police report about Eric Harris' Internet ravings.^[15][16][17] This lawsuit was dismissed along with several others pertaining to the shooting.^[18]

Politics

Jefferson County was a Republican stronghold for most of the 20th century. However, it has voted Democratic in every presidential election since 2008, consistent with the general trend in the Denver metropolitan area. In 2020, Joe Biden won the largest percentage for a Democratic presidential candidate since 1916.

Recreation

State parks

• Chatfield State Park
• Golden Gate Canyon State Park
• Staunton State Park

National forests and wilderness

• Pike National Forest
• Roosevelt National Forest
• Lost Creek Wilderness

National wildlife refuges

• Rocky Flats National Wildlife Refuge
• Two Ponds National Wildlife Refuge

Historic trail

• South Platte Trail

Recreational trails

• American Discovery Trail
• Apex National Recreation Trail
• Big Dry Creek National Recreation Trail
• Colorado Trail
• Platte River Greenway National Recreation Trail
• Two Ponds National Recreation Trail

Scenic byway

• Lariat Loop Scenic and Historic Byway

Golf course

• Hiwan Golf Club

• Indian Tree Golf Club

Communities

Cities

Towns

Census-designated places

Unincorporated communities