Boulder County, Colorado

Boulder County is a county in Colorado, United States, about 25 miles northwest of Denver at
the base of the Rocky Mountains’ Front Range. It had a population of 330,758 at the 2020 census,
an estimated 328,560 by 2024, and covers 726 square miles (1,880 km2) centred near 40°05′N 105°22′W.

Boulder is the county seat and the county’s most populous city; its postal code is 80301. The
county holds 4 cities, 6 incorporated towns and dozens of unincorporated mountain communities and
census-designated places, and it runs on Mountain Time. Its FIPS code is 08013.

Towns & Villages in Boulder County

Boulder County has 10 incorporated municipalities — 4 cities and 6 statutory towns —
plus 24 census-designated places (CDPs) and a scatter of unincorporated mountain communities with
no city government of their own. The table below covers every incorporated place plus the three
CDPs with a separately tabulated 2020 population.

Two places on this list straddle county lines. Longmont’s population figure above is
citywide — most of the city sits in Boulder County, with the remainder extending east into
Weld County. Erie runs the same way: the Census Bureau counted 58 percent of its 2020 residents
in Weld County and the other 42 percent, 12,651 people, in Boulder County.

Beyond that table, Boulder County has 21 more CDPs on record — among them Allenspark,
Altona, Coal Creek, Eldora, Gold Hill, Pine Brook Hill, Sugarloaf and Sunshine — and a set
of unincorporated communities including Caribou, Canfield, Gooding, Highland, Hygiene, Liggett,
Morey, Pinecliffe, Pleasant View Ridge and Tabor. Most began as 19th-century mining camps or
railroad sidings in the mountain canyons west of Boulder; the Census Bureau does not tabulate
population separately for them.

Geography

Boulder County spans the transition from the high plains to the Rocky Mountains’ Front Range,
running from flat farmland in its eastern third up through foothills to peaks above 13,000 feet
along its western edge. Of its 726 square miles, about 712 are land and 14 are water. Boulder
Creek and the St. Vrain Creek drainages carry most of that surface water down from the
mountains, and the Indian Peaks Wilderness covers much of the county’s high country along the
Continental Divide.

Larimer County lies to the north, Weld County to the east, Broomfield and Jefferson counties
to the south, Gilpin County to the southwest, and Grand County to the west. Larimer County, Weld County, Jefferson County, Gilpin County and Grand County all border Boulder directly;
the City and County of Broomfield, carved out in 2001, also shares a short southeastern border
but has no separate county post on this site.

Demographics

Boulder County had a population of 330,758 at the 2020 census, and the latest estimate puts
the county near 328,560 residents, a slight decline. Boulder and Longmont are by far the two
largest communities, together holding well over half the county’s population. Colorado’s
statewide median household income was $92,911 in the 2023 ACS; Boulder County’s own figure runs
higher in most of its towns — Niwot alone reported a 2020 median household income of
$118,914. Population density works out to roughly 465 people per square mile of land, reflecting
the county’s concentration along the Front Range corridor between Boulder and Longmont, with the
mountainous western half sparsely settled.

Economy & Local Life

Research, education and technology dominate the county’s economy. The University of Colorado
Boulder is the single largest employer, with about 6,200 staff, followed by Ball Corporation at
roughly 4,800 and Boulder Valley School District at about 3,832. Three federal research labs
cluster in Boulder itself: the National Center for Atmospheric Research, the National Oceanic
and Atmospheric Administration, and the National Institute of Standards and Technology, all
drawing scientists and engineers into the county. Lafayette and Louisville trace their roots to
coal mining before shifting to suburban residential life once the mines closed; Louisville today
hosts two hospitals, AdventHealth Avista and Centennial Peaks. Nederland, in the mountains west
of Boulder, runs on tourism tied to the Eldora Mountain Resort ski area and draws crowds each
March for the Frozen Dead Guy Days festival.

History

The Colorado territorial legislature organized Boulder County on 1 November 1861, one of the
territory’s original 17 counties. Prospectors had already been working the area since the 1859
Gold Rush, and the county’s name comes from the large granite boulders scattered along Boulder
Creek at the base of the foothills. The land had been Arapaho territory before the rush; Chief
Niwot, whose name means “left-handed,” led the band that met the first gold-seeking settlers in
1858, and the CDP of Niwot carries his name today.

On 30 December 2021, the Marshall Fire burned through unincorporated Boulder County,
Louisville and Superior, destroying 991 homes and damaging 127 more across the three areas. It
is the most destructive wildfire in Colorado history by structures lost, and Superior and
Louisville are still rebuilding entire subdivisions more than four years later.

Getting There

US 36 runs from Denver through Broomfield into Boulder and continues northwest as the
Boulder-Estes Park corridor; no interstate highway crosses the county directly, though I-25
skirts its eastern edge in neighboring Weld County. State Highway 119 links Boulder to Longmont
and continues into the mountains toward Nederland as the Peak to Peak Highway, and US 287 runs
north-south through Lafayette and Longmont.

• Denver — about 25 miles southeast
• Fort Collins — about 30 miles north
• Golden — about 20 miles south
• Estes Park — about 30 miles northwest

Denver International Airport, roughly 45 miles southeast of Boulder, is the nearest major
commercial airport. Amtrak does not serve Boulder County directly; the closest station is
Denver’s Union Station, connected to Boulder and Longmont by regional bus service.

Frequently Asked Questions

Where is Boulder County located?
It sits along Colorado’s Front Range at the base of the Rocky Mountains, about 25 miles
northwest of Denver, bordered by Larimer, Weld, Broomfield, Jefferson, Gilpin and Grand
counties.

What is the population of Boulder County?
330,758 at the 2020 census, with a 2024 estimate near 328,560.

How big is Boulder County?
726 square miles (1,880 km2), of which about 712 square miles are land.

What is the county seat of Boulder County?
Boulder, the county’s largest city with 108,250 residents.

How many towns and cities are in Boulder County?
Ten incorporated municipalities — the cities of Boulder, Longmont, Lafayette and Louisville,
plus the towns of Erie, Superior, Lyons, Nederland, Jamestown and Ward — along with 24 CDPs
and numerous unincorporated mountain communities.

What ZIP codes does Boulder County use?
80301 for Boulder, 80501 for Longmont, 80026 for Lafayette, 80516 for Erie, 80027 for Louisville
and Superior, 80503 for Niwot, and 80466 for Nederland.

What is Boulder County known for?
The University of Colorado Boulder, federal research labs including NOAA and NCAR, and the
December 2021 Marshall Fire, the most destructive wildfire in Colorado’s history.

More counties in this state: Towns
and villages in Colorado.