Summit County is a county located in the U.S. state of Colorado. As of the 2020 census, the population was 31,055. The county seat and largest town is Breckenridge.

Summit County comprises the Breckenridge, CO Micropolitan Statistical Area.

Summit County was organized as one of the seventeen original Colorado counties by the First Territorial Legislature on November 1, 1861. It was named for the many mountain summits in the county. Until February 2, 1874, its boundaries included the area now comprising Summit County, Grand County, Routt County, Moffat County, Garfield County, Eagle County, and Rio Blanco County.

In 1874, the northern half of the original Summit County was split off to form Grand County; with the creation of Garfield and Eagle counties in 1883, Summit County arrived at its present boundaries. In addition, Summit County has seen two major boom eras.

According to the U.S. Census Bureau, the county has a total area of 619 square miles (1,600 km), of which 608 square miles (1,570 km) is land and 11 square miles (28 km) (1.8%) is water.

The terrain of the county is mountainous with elevations ranging from 7,957 feet (2,425 m) at Green Mountain Reservoir to 14,270 feet (4,350 m) at Grays Peak. The elevation of the county seat of Breckenridge is 9,602 feet (2,927 m), making it one of the highest cities in the state of Colorado and the United States. Much of the county has an alpine climate (ET in the Köppen Classification) characterized by tundra vegetation. Breckenridge and other similar elevations in the county have a subarctic climate (Dfc) characterized by cool summers and abundant snowfall in winter.

• Grand County – north
• Clear Creek County – east
• Park County – southeast
• Lake County – southwest
• Eagle County – west

• Interstate 70
• I-70 BL
• U.S. Highway 6
• State Highway 9
• State Highway 91

Historical population

Census	Pop.	Note	%±
1870	258		—
1880	5,459		2,015.9%
1890	1,906		−65.1%
1900	2,744		44.0%
1910	2,003		−27.0%
1920	1,724		−13.9%
1930	987		−42.7%
1940	1,754		77.7%
1950	1,135		−35.3%
1960	2,073		82.6%
1970	2,665		28.6%
1980	8,848		232.0%
1990	12,281		38.8%
2000	23,548		91.7%
2010	27,994		18.9%
2020	31,055		10.9%
2023 (est.)	30,465		−1.9%
U.S. Decennial Census 1790–1960 1900–1990 1990–2000 2010–2020

As of the census of 2000, there were 23,548 people, 9,120 households, and 4,769 families residing in the county. The population density was 39 people per square mile (15 people/km). There were 24,201 housing units at an average density of 40 per square mile (15/km). The racial makeup of the county was 91.84% White, 0.68% Black or African American, 0.48% Native American, 0.87% Asian, 0.07% Pacific Islander, 3.96% from other races, and 2.10% from two or more races. 9.79% of the population were Hispanic or Latino of any race.

There were 9,120 households, out of which 24.00% had children under the age of 18 living with them, 44.00% were married couples living together, 4.40% had a female householder with no husband present, and 47.70% were non-families. 21.60% of all households were made up of individuals, and 1.60% had someone living alone who was 65 years of age or older. The average household size was 2.48 and the average family size was 2.86.

In the county, the population was spread out, with 17.40% under the age of 18, 15.70% from 18 to 24, 44.30% from 25 to 44, 19.40% from 45 to 64, and 3.30% who were 65 years of age or older. The median age was 31 years. As of 2014, the life expectancy in Summit County was 86.83 years, the longest average life expectancy of any county in the United States. For every 100 females there were 139.00 males. For every 100 females age 18 and over, there were 144.90 males.

The median income for a household in the county was $56,587, and the median income for a family was $66,914 (these figures had risen to $65,281 and $80,441 respectively as of a 2007 estimate). Males had a median income of $33,741 versus $27,017 for females. The per capita income for the county was $28,676. About 3.10% of families and 9.00% of the population were below the poverty line, including 4.30% of those under age 18 and 3.40% of those age 65 or over.

The 2019 average real estate prices in Summit County were $1,262,929 for a single family home, $559,776 for a condo, townhome or duplex and $344,945 for a vacant piece of land (YTD through December 2019).

According to a report in the Journal of the American Medical Association, residents of Summit County had a 2014 life expectancy from birth of 86.83 years in 2014, the longest in the United States. Both men and women live longer in Summit County than in any other county in the United States: 85.5 years for men and 88.0 years for women is the life expectancy at birth. Two contiguous counties, Pitkin and Eagle counties, rank numbers two and three in the nation in life expectancy. Factors contributing to the high life expectancy in Summit County are "high education, high income, high access to medical care, the people are physically active, obesity is lower than anywhere else — so you’re doing it right,” said Dr. Ali Mokdad, one of the study's co-authors.

• Breckenridge Elementary School
• Dillon Valley Elementary School (Dillon)
• Frisco Elementary School
• Silverthorne Elementary School
• Summit Cove Elementary School (Dillon)
• Upper Blue Elementary School (Breckenridge)

• Summit Middle School (Frisco)

• Snowy Peaks Junior/Senior High School (Frisco)
• Summit High School (Breckenridge)

Colorado Mountain College operates campuses in Breckenridge and Dillon.

Summit County is liberal in most elections. As of the 2020 presidential election, Summit County has not voted for the Republican candidate since 1988.

United States presidential election results for Summit County, Colorado

Year	Republican		Democratic		Third party(ies)
	No.	%	No.	%	No.	%
2024	5,244	29.89%	11,762	67.04%	539	3.07%
2020	5,322	28.80%	12,631	68.35%	526	2.85%
2016	5,100	31.53%	9,557	59.09%	1,517	9.38%
2012	5,571	36.38%	9,347	61.04%	394	2.57%
2008	4,883	32.77%	9,802	65.79%	214	1.44%
2004	5,370	39.10%	8,144	59.29%	221	1.61%
2000	4,497	40.63%	5,304	47.92%	1,267	11.45%
1996	3,261	38.73%	3,970	47.16%	1,188	14.11%
1992	2,256	26.95%	3,344	39.95%	2,770	33.09%
1988	2,893	51.44%	2,595	46.14%	136	2.42%
1984	3,253	66.14%	1,588	32.29%	77	1.57%
1980	2,027	46.54%	1,285	29.51%	1,043	23.95%
1976	1,826	58.15%	1,087	34.62%	227	7.23%
1972	1,082	59.03%	707	38.57%	44	2.40%
1968	536	57.39%	301	32.23%	97	10.39%
1964	344	41.55%	483	58.33%	1	0.12%
1960	424	51.27%	400	48.37%	3	0.36%
1956	429	64.61%	235	35.39%	0	0.00%
1952	442	61.90%	271	37.96%	1	0.14%
1948	292	43.26%	378	56.00%	5	0.74%
1944	326	57.60%	237	41.87%	3	0.53%
1940	479	46.78%	540	52.73%	5	0.49%
1936	268	34.85%	496	64.50%	5	0.65%
1932	224	34.78%	397	61.65%	23	3.57%
1928	362	53.16%	306	44.93%	13	1.91%
1924	354	47.52%	241	32.35%	150	20.13%
1920	418	50.36%	388	46.75%	24	2.89%
1916	268	26.27%	717	70.29%	35	3.43%
1912	179	18.55%	600	62.18%	186	19.27%
1908	366	31.99%	743	64.95%	35	3.06%
1904	561	48.15%	569	48.84%	35	3.00%
1900	394	28.59%	967	70.17%	17	1.23%
1896	28	2.20%	1,243	97.64%	2	0.16%
1892	279	25.60%	0	0.00%	811	74.40%
1888	701	55.63%	557	44.21%	2	0.16%
1884	609	51.92%	556	47.40%	8	0.68%
1880	1,289	48.81%	1,328	50.28%	24	0.91%

• Blue River
• Breckenridge
• Dillon
• Frisco
• Keystone
• Montezuma
• Silverthorne

• Copper Mountain
• Heeney

• Dyersville
• Kokomo
• Parkville
• Preston
• Saints John
• Tiger

• White River National Forest
• Eagles Nest Wilderness

• Arapahoe Basin
• Breckenridge
• Copper Mountain
• Keystone

• American Discovery Trail
• Colorado Trail
• Continental Divide National Scenic Trail
• Great Parks Bicycle Route
• Top of the Rockies National Scenic Byway
• TransAmerica Trail Bicycle Route
• Vail Pass National Recreation Trail
• Wheeler Ten Mile National Recreation Trail

The county has three reservoirs, Lake Dillon, Green Mountain Reservoir, and Clinton Gulch Dam Reservoir that are also popular recreation sites.

• Silver Dollar Island

• Dillon Amphitheater

• Bibliography of Colorado
• Geography of Colorado
• History of Colorado
  • National Register of Historic Places listings in Summit County, Colorado
• Index of Colorado-related articles
• List of Colorado-related lists
  • List of counties in Colorado
  • List of statistical areas in Colorado
• Outline of Colorado

• Official website
• Colorado County Evolution by Don Stanwyck
• Colorado Historical Society
• Kokomo and Racen ghost towns

39°30′N 106°03′W / 39.50°N 106.05°W / 39.50; -106.05