Largest Counties in Colorado

A territory formed during the Pike’s Peak Gold Rush, Colorado became a state in 1876. Known for its mining history and the Rocky Mountains, Colorado has 64 counties.

10 Largest Counties in Colorado

1. El Paso County

County Facts:

  • Population: Approximately 730,000
  • Area Codes: 719
  • Zip Codes: 80808, 80831, 80832, 80840, 80901-80951
  • County Seat: Colorado Springs

Geography and History:

El Paso County, located in central Colorado, covers 2,130 square miles. The county features a diverse landscape, ranging from the plains in the east to the towering peaks of the Rocky Mountains in the west, with Pikes Peak dominating the skyline. The region experiences a semi-arid climate with mild winters and warm summers.

The county was established in 1861 as one of the original 17 counties of Colorado Territory. Colorado Springs, founded in 1871 by General William J. Palmer, quickly became a major resort town, attracting visitors to its natural beauty and proximity to Pikes Peak. The region grew rapidly with the advent of the railroad, mining, and military installations, including Fort Carson and the United States Air Force Academy.

Colleges and Universities:

  • University of Colorado Colorado Springs (UCCS): A large public university offering undergraduate, graduate, and doctoral programs.
  • Colorado College: A private liberal arts institution in Colorado Springs known for its innovative Block Plan curriculum.
  • Pikes Peak State College: Offers associate degrees and vocational training, serving the local community with accessible education.

Major Landmarks:

Pikes Peak is the county’s most iconic landmark, attracting hikers and tourists to its 14,115-foot summit. Garden of the Gods, a National Natural Landmark, features stunning red rock formations, while the United States Air Force Academy is a significant historical and architectural site. The Colorado Springs Pioneer Museum highlights the region’s rich history.


2. Denver County

County Facts:

  • Population: Approximately 715,000
  • Area Codes: 303, 720
  • Zip Codes: 80012, 80123, 80202, 80203, 80204, 80209, 80211, 80219, 80222
  • County Seat: Denver

Geography and History:

Denver County, encompassing the city of Denver, spans 155 square miles. The geography of the area is characterized by its location on the high plains at an elevation of 5,280 feet, earning it the nickname “Mile-High City.” The county enjoys a semi-arid climate with four distinct seasons and over 300 days of sunshine annually.

Denver was founded during the Pike’s Peak Gold Rush in 1858, quickly growing as a mining supply town. It became the territorial capital in 1867 and the state capital in 1881. Denver has since evolved into a major metropolitan area and economic hub for the Rocky Mountain region, with industries ranging from energy and aerospace to healthcare and technology.

Colleges and Universities:

  • University of Denver (DU): A private university offering a broad range of undergraduate and graduate programs.
  • Metropolitan State University of Denver (MSU Denver): A public university known for its focus on accessibility and career-oriented education.
  • Community College of Denver (CCD): Provides two-year degrees, certificates, and transfer programs to local students.

Major Landmarks:

The Colorado State Capitol, with its iconic gold dome, is a central landmark. Denver is home to the Denver Art Museum, Denver Botanic Gardens, and Coors Field, where the Colorado Rockies play. Larimer Square and the historic Union Station are also major attractions, showcasing the city’s vibrant history and modern growth.


3. Arapahoe County

County Facts:

  • Population: Approximately 656,000
  • Area Codes: 303, 720
  • Zip Codes: 80012, 80013, 80014, 80015, 80016, 80112, 80121, 80122, 80123, 80138
  • County Seat: Littleton

Geography and History:

Arapahoe County spans 805 square miles in eastern Colorado, with terrain ranging from the urbanized Denver suburbs to the wide-open plains further east. The county experiences a semi-arid climate with distinct seasonal variations.

Named after the Arapaho Native American tribe, the county was one of the original 17 counties of Colorado, established in 1861. Littleton became the county seat in 1904, and the county’s development has been closely tied to the expansion of the Denver metropolitan area. Arapahoe County’s growth accelerated in the mid-20th century as the suburbs of Denver expanded into the area.

Colleges and Universities:

  • Arapahoe Community College (ACC): Offers a wide range of associate degrees, certifications, and transfer opportunities to students in the Denver metro area.
  • Colorado State University Global Campus: Specializes in online programs for adult learners, providing bachelor’s and master’s degrees.
  • University of Denver (DU): Nearby in Denver, DU serves many Arapahoe County residents.

Major Landmarks:

Cherry Creek State Park, with its large reservoir, offers recreation and outdoor activities. The Littleton Museum, located in the county seat, preserves the area’s pioneer history, while the nearby High Line Canal Trail provides scenic pathways for biking and hiking. The county is also home to the Denver Tech Center, a major business district.


4. Jefferson County

County Facts:

  • Population: Approximately 585,000
  • Area Codes: 303, 720
  • Zip Codes: 80002, 80005, 80127, 80128, 80401, 80403, 80465
  • County Seat: Golden

Geography and History:

Jefferson County, located west of Denver, covers 774 square miles, ranging from urban suburbs to the foothills of the Rocky Mountains. The county’s diverse geography includes flat plains, rolling hills, and mountainous terrain. It has a semi-arid climate with cold winters and warm summers.

Jefferson County was named after Thomas Jefferson and was one of the original counties created in Colorado Territory in 1861. Golden, the county seat, was a gold rush town that grew quickly in the late 19th century. It became a regional hub for mining and industry, with the Colorado School of Mines becoming a key institution in the area. The county’s proximity to Denver has spurred suburban growth, making it one of the most populous counties in Colorado.

Colleges and Universities:

  • Colorado School of Mines: A prestigious public research university specializing in engineering and applied sciences.
  • Red Rocks Community College (RRCC): Offers two-year degrees and vocational training with campuses in Lakewood and Arvada.
  • Rocky Mountain College of Art and Design (RMCAD): A private college in Lakewood offering specialized art and design programs.

Major Landmarks:

Red Rocks Amphitheatre, known for its natural acoustics and stunning setting, is one of the county’s most famous landmarks. The Coors Brewery in Golden, the largest single-site brewery in the world, is another major attraction. The scenic Lariat Loop Byway offers a journey through the county’s mountain landscapes, including stops at Lookout Mountain and Buffalo Bill’s Museum and Grave.


5. Adams County

County Facts:

  • Population: Approximately 520,000
  • Area Codes: 303, 720
  • Zip Codes: 80022, 80031, 80011, 80017, 80136, 80601, 80602, 80640
  • County Seat: Brighton

Geography and History:

Adams County, located in the northern Denver metropolitan area, covers 1,184 square miles. The county features flat plains in the east and suburban areas in the west. The climate is semi-arid, with hot summers and cold winters, typical of the Colorado Front Range.

Established in 1901, the county was named after Alva Adams, a former governor of Colorado. Brighton became the county seat in 1904, and the area developed as an agricultural hub due to its fertile soil and irrigation systems. As Denver expanded, Adams County transformed from farmland to a suburban area, driven by industrial growth, particularly around Denver International Airport.

Colleges and Universities:

  • Front Range Community College (FRCC): Provides associate degrees and technical certifications, serving the northern Denver metro area.
  • Community College of Aurora (CCA): Offers two-year degrees and workforce development programs, accessible to Adams County residents.
  • University of Colorado Denver (CU Denver): Located nearby, CU Denver offers a wide range of undergraduate and graduate programs.

Major Landmarks:

Barr Lake State Park is a key outdoor destination, offering birdwatching, fishing, and hiking opportunities. The Adams County Fairgrounds host the annual Adams County Fair, showcasing the area’s agricultural roots. Brighton’s historic downtown area features preserved 19th-century buildings, while Denver International Airport, located in Adams County, is a critical transportation hub for the region.


6. Larimer County

County Facts:

  • Population: Approximately 365,000
  • Area Codes: 970
  • Zip Codes: 80521, 80524, 80525, 80526, 80528, 80535, 80537
  • County Seat: Fort Collins

Geography and History:

Larimer County, in northern Colorado, spans 2,634 square miles, with landscapes ranging from the Great Plains to the peaks of the Rocky Mountains. The county includes parts of Rocky Mountain National Park and Roosevelt National Forest, offering a wide range of outdoor activities. The climate is semi-arid with cold winters and warm summers.

The county was established in 1861 and named after William Larimer, a founder of Denver. Fort Collins, originally a military fort, grew into a center of agriculture and education with the establishment of Colorado State University. The county has a rich history tied to early pioneers, agriculture, and outdoor recreation.

Colleges and Universities:

  • Colorado State University (CSU): A major public research university offering a wide array of programs in fields like agriculture, business, engineering, and health sciences.
  • Front Range Community College (FRCC): Provides associate degrees and certificates with a campus in Fort Collins.
  • Institute of Business and Medical Careers (IBMC): A vocational institution offering career-focused programs in healthcare and business.

Major Landmarks:

Rocky Mountain National Park is the county’s most famous landmark, attracting millions of visitors annually to its stunning mountain landscapes. Fort Collins’ Old Town district is another popular destination, with historic buildings, shops, and restaurants. Horsetooth Reservoir, located just west of Fort Collins, is a major recreational spot for boating, fishing, and hiking.


7. Douglas County

County Facts:

  • Population: Approximately 370,000
  • Area Codes: 303, 720
  • Zip Codes: 80104, 80108, 80109, 80134, 80138
  • County Seat: Castle Rock

Geography and History:

Douglas County, situated between Denver and Colorado Springs, covers 844 square miles. The county’s terrain features a mix of rolling plains and foothills, with the Rampart Range providing a scenic backdrop. The county experiences a semi-arid climate, with warm summers and cold winters.

Founded in 1861, Douglas County was named after U.S. Senator Stephen A. Douglas. The county’s history is closely tied to the development of the Denver and Rio Grande Railroad and the rise of ranching and farming in the late 19th century. More recently, the county has seen rapid suburban growth due to its proximity to Denver and Colorado Springs.

Colleges and Universities:

  • Arapahoe Community College (ACC): Offers associate degrees and career-focused programs with a campus in Parker, serving Douglas County residents.
  • University of Colorado Denver (CU Denver): Located nearby in Denver, offering a wide range of undergraduate and graduate programs.
  • Colorado Christian University (CCU): A private Christian institution with campuses throughout Colorado, serving students in Douglas County.

Major Landmarks:

Castle Rock, the large butte that the town is named after, is one of the county’s most iconic natural landmarks, offering hiking and scenic views. The 12-mile stretch of the Cherry Creek Trail running through the county is popular for biking and walking. Roxborough State Park, with its striking red rock formations, is another major destination for outdoor enthusiasts.


8. Boulder County

County Facts:

  • Population: Approximately 330,000
  • Area Codes: 303, 720
  • Zip Codes: 80301, 80302, 80303, 80304, 80305, 80501, 80503, 80504
  • County Seat: Boulder

Geography and History:

Boulder County spans 740 square miles, located in the foothills of the Rocky Mountains. The county is known for its scenic beauty, with towering mountains, open plains, and the Boulder Creek running through the heart of the city. The county experiences a semi-arid climate with mild winters and warm summers.

Established in 1861, Boulder County was one of the original counties in Colorado. The city of Boulder quickly grew as a mining supply town and later as an educational and cultural center with the establishment of the University of Colorado. The county has long been associated with outdoor recreation, environmentalism, and progressive politics.

Colleges and Universities:

  • University of Colorado Boulder (CU Boulder): The flagship campus of the University of Colorado system, offering a wide range of undergraduate, graduate, and doctoral programs.
  • Naropa University: A private institution focused on contemplative education, offering programs in the arts, psychology, and religious studies.
  • Front Range Community College (FRCC): Provides associate degrees and technical certifications with a campus in Longmont.

Major Landmarks:

The Flatirons, the iconic rock formations overlooking Boulder, are a major outdoor landmark, attracting hikers and rock climbers. The Pearl Street Mall in downtown Boulder is a hub for shopping, dining, and entertainment. Boulder Creek Path offers scenic views of the creek and the surrounding mountains, while the historic Chautauqua Park provides hiking trails and cultural programming.


9. Weld County

County Facts:

  • Population: Approximately 330,000
  • Area Codes: 970
  • Zip Codes: 80601, 80631, 80634, 80643, 80645, 80651, 80729
  • County Seat: Greeley

Geography and History:

Weld County covers 4,017 square miles, making it one of the largest counties in Colorado. The terrain is mostly flat and agricultural, with the South Platte River running through the eastern part of the county. Weld County experiences a semi-arid climate, with hot summers and cold winters.

Named after Lewis Ledyard Weld, the county was founded in 1861 and has long been associated with agriculture, particularly cattle ranching and farming. The county seat, Greeley, was established as a utopian agricultural community in the late 19th century and has grown into a regional economic center.

Colleges and Universities:

  • University of Northern Colorado (UNC): A public university located in Greeley, offering programs in education, business, and health sciences.
  • Aims Community College: Provides associate degrees and technical certifications, serving the northern Colorado region with multiple campuses.
  • Front Range Community College (FRCC): Offers additional educational opportunities to Weld County residents.

Major Landmarks:

The Pawnee National Grassland is a major outdoor attraction in Weld County, offering hiking, birdwatching, and scenic drives. The Greeley History Museum and Centennial Village preserve the area’s pioneer and agricultural history. The Weld County Fair is another highlight, showcasing the county’s strong agricultural roots.


10. Pueblo County

County Facts:

  • Population: Approximately 170,000
  • Area Codes: 719
  • Zip Codes: 81001, 81003, 81004, 81005, 81006, 81007, 81008
  • County Seat: Pueblo

Geography and History:

Pueblo County spans 2,398 square miles in southern Colorado, with geography ranging from the arid plains to the Arkansas River Valley. The county’s climate is semi-arid, with hot summers and mild winters, typical of southern Colorado’s high desert region.

Founded in 1861, Pueblo County grew as an industrial hub, particularly with the establishment of the Colorado Fuel and Iron Company’s steel mill, which made Pueblo a center of steel production in the West. The county has a rich history tied to mining, agriculture, and industry, and it remains an important cultural and economic center in southern Colorado.

Colleges and Universities:

  • Colorado State University Pueblo (CSU Pueblo): A regional public university offering a wide range of undergraduate and graduate programs.
  • Pueblo Community College (PCC): Offers associate degrees, certifications, and technical training, serving southern Colorado.
  • University of Colorado Colorado Springs (UCCS): Provides distance education and continuing education opportunities to Pueblo County residents.

Major Landmarks:

The Historic Arkansas Riverwalk of Pueblo is a major cultural and recreational landmark, offering scenic boat rides, dining, and public art. The Pueblo Weisbrod Aircraft Museum highlights the area’s military history, while the Steelworks Museum preserves the history of the steel industry in Pueblo. Lake Pueblo State Park is a popular destination for boating, fishing, and camping.