Jefferson County is a county in Colorado, United States, on the Front Range of the Rocky Mountains immediately west of Denver. It had a population of 582,910 at the 2020 census and covers 774 square miles (2,004 km2) centred near 39°35′N 105°15′W, making it the fourth most populous county in the state.
Golden is the county seat, and its postal code is 80401. The county contains seven cities, five towns, and more than a dozen unincorporated communities and census-designated places, spread across the plains around Denver and the foothill canyons toward the mountains. Jefferson County is Mountain Time (UTC-7, UTC-6 during daylight saving) and its FIPS code is 08059.
Towns & Villages in Jefferson County
Lakewood is the county’s largest city; several other municipalities, including Arvada, Littleton, Westminster, Bow Mar, and Superior, extend into Jefferson County from a home base in a neighboring county. Unincorporated mountain communities such as Evergreen, Conifer, and Ken Caryl have no city government of their own but function as recognized census-designated places (CDP) with their own post offices. Places marked Unincorp. have no municipal government.
| Place | Type | Pop. | ZIP |
|---|---|---|---|
| Lakewood | City | 155,984 | 80226 |
| Arvada | City (part) | — | 80002 |
| Westminster | City (part) | — | — |
| Wheat Ridge | City | — | 80033 |
| Golden | City · seat | 20,399 | 80401 |
| Littleton | City (part) | — | — |
| Edgewater | City | — | 80214 |
| Superior | Town (part) | — | — |
| Morrison | Town | — | 80465 |
| Mountain View | Town | — | — |
| Lakeside | Town | — | — |
| Bow Mar | Town (part) | — | — |
| Evergreen | CDP | — | 80439 |
| Conifer | CDP | — | 80433 |
| Ken Caryl | CDP | — | — |
| Columbine | CDP | — | — |
| Applewood | CDP | — | — |
| Dakota Ridge | CDP | — | — |
| Fairmount | CDP | — | — |
| Genesee | CDP | — | — |
| Aspen Park | Unincorp. | — | — |
| Indian Hills | Unincorp. | — | 80454 |
| Kittredge | Unincorp. | — | 80457 |
| Idledale | Unincorp. | — | 80453 |
| Pine | Unincorp. | — | 80470 |
| Pine Junction | Unincorp. | — | — |
| Buffalo Creek | Unincorp. | — | — |
| Foxton | Unincorp. | — | — |
Several places in the county share a name with a similarly named place elsewhere on the Front Range — Littleton, Arvada, and Westminster are all seated in a neighboring county and only their outer edges cross into Jefferson County. Broomfield, sometimes assumed to border Jefferson County’s towns, is in fact its own consolidated city-and-county and is not part of Jefferson County at all.
ZIP Codes
- 80401 — Golden (also serves the CU/Colorado School of Mines campus area)
- 80439 — Evergreen
- 80433 — Conifer
- 80465 — Morrison
- 80454 — Indian Hills
- 80457 — Kittredge
- 80453 — Idledale
- 80470 — Pine (also serves Buffalo Creek and Pine Junction)
- 80033 — Wheat Ridge
- 80002 — Arvada (the portion in Jefferson County)
- 80214 — Edgewater
Lakewood spans several ZIP codes (including 80226, 80215, and 80228) since it is the county’s largest city; the smaller CDPs west of Ken Caryl and Columbine generally share Denver-metro ZIP codes rather than a dedicated one of their own.
Geography
Jefferson County straddles the boundary between the Great Plains and the Rocky Mountains. Its eastern third, the Denver suburbs, is flat to gently rolling grassland; its western two-thirds climb through foothill canyons — Clear Creek Canyon, Bear Creek Canyon, and the South Platte River canyon near Buffalo Creek and Pine — toward peaks over 10,000 feet along the Continental Divide foothills. Clear Creek and Bear Creek both flow east out of the mountains through the county to join the South Platte River near Denver. Red Rocks Park, home of the Red Rocks Amphitheatre, sits on the county’s dramatic sandstone formations near Morrison.
Jefferson County borders Boulder County to the north, Denver County and Arapahoe County to the east, Teller County to the south, Park County to the southwest, Clear Creek County to the west, and Gilpin County to the northwest. Adams County lies to the northeast and Douglas County to the southeast; both border only a short stretch of Jefferson County’s eastern edge. Broomfield, a separate consolidated city-and-county, adjoins the county’s far northeast corner.
Demographics
Jefferson County had 582,910 residents at the 2020 census, the fourth-highest county total in Colorado. Lakewood, with roughly 156,000 residents, and Arvada’s Jefferson County portion are the two largest population centers. Median household income in the county runs above the Colorado median of $92,911, reflecting the mix of established Denver-metro suburbs and higher-income mountain communities such as Evergreen and Ken Caryl. Population density is about 763 people per square mile, concentrated overwhelmingly in the eastern, flatter portion of the county.
Economy & Local Life
The Denver Federal Center in Lakewood is the largest concentration of federal government offices outside Washington, D.C., and is one of the county’s biggest employers. Coors Brewing Company, headquartered in Golden, has operated its main brewery there since 1873 and remains a major private employer and tourist draw. The Colorado School of Mines, also in Golden, anchors the county’s higher-education and engineering-research sector. Red Rocks Amphitheatre near Morrison hosts a nationally known concert season each summer and is one of the county’s biggest annual visitor draws.
History
Jefferson County was organized on November 1, 1861, one of the original 17 counties created when the Colorado Territory was formed, and takes its name from the short-lived Jefferson Territory, an unofficial provisional government set up by Front Range settlers in 1859 in honor of Thomas Jefferson before Congress created Colorado Territory. Golden served as the territorial capital of Colorado from 1862 to 1867, before the capital moved to Denver. Gold discoveries in the foothill canyons in the late 1850s and 1860s drove the county’s earliest mining-era settlement, and the arrival of the railroads through Golden and Morrison later in the 19th century shifted the economy toward quarrying, brewing, and eventually Denver-suburb residential growth through the 20th century.
Getting There
Interstate 70 crosses the county east–west through Golden and the mountain canyons; US Route 6 and US Route 285 provide the other main routes through the foothills and toward South Park. C-470 loops along the county’s southern and eastern edge, connecting to Interstate 25.
- Denver — 12 miles east
- Boulder — 20 miles northeast
- Colorado Springs — 55 miles south
- Fairplay — 45 miles southwest
Denver International Airport, about 35 miles from Golden, is the nearest major commercial airport; Rocky Mountain Metropolitan Airport in Broomfield, just north of the county, handles general aviation.
Frequently Asked Questions
Where is Jefferson County, Colorado?
It sits immediately west of Denver on the Front Range, stretching from the eastern Denver suburbs into the foothills of the Rocky Mountains.
What is the population of Jefferson County?
582,910 as of the 2020 census, the fourth-highest total among Colorado’s 64 counties.
How big is Jefferson County?
774 square miles (2,004 km2), most of it foothill and mountain terrain west of the Denver-metro plains.
What is the county seat of Jefferson County?
Golden is the county seat; Lakewood is the county’s largest city.
How many towns and cities are in Jefferson County?
Seven cities and five towns lie fully or partly within the county, alongside more than a dozen unincorporated communities and CDPs in the foothills.
What ZIP codes are in Jefferson County?
Golden is 80401; mountain communities include Evergreen (80439), Conifer (80433), and Morrison (80465), among others.
Is Red Rocks Amphitheatre in Jefferson County?
Yes. Red Rocks Park and Amphitheatre sits on county-owned land near Morrison, on the eastern edge of the foothills.
More counties in this state: Towns and villages in Colorado.