County outline
Where Summit County is located
Area breakdown
Land accounts for 98.2% of Summit County’s measured area and water for 1.8%. Its combined area converts to 1,603.9 square kilometers or approximately 396,326 acres.
Green: land · blue: water
| Measurement | Square miles | Square kilometers | Acres |
|---|---|---|---|
| Land | 608.328 | 1,575.562 | 389,329.9 |
| Water | 10.931 | 28.311 | 6,995.8 |
| Total | 619.259 | 1,603.873 | 396,325.8 |
How Summit County compares
By original Census land area, Summit County ranks #55 of 64 in Colorado and #1595 of 3,222 nationally. National rankings include the 50 states, District of Columbia, and Puerto Rico.
Its land area is 0.425 times the Colorado county-equivalent median of 1,431.5 square miles. It accounts for 0.6% of the combined county land area in the state.
See the complete Colorado ranking · What counts as a county equivalent?
Population and density of Summit County
The Census Bureau estimates that 31,517 people lived in Summit County on July 1, 2025. That ranks #1,442 of 3,222 county equivalents nationally and #19 of 64 in Colorado. Since the April 1, 2020 estimates base of 31,289, the population has grown by 228 (+0.7%), compared with +4.1% for Colorado as a whole.
With 608.3 square miles of land, that is 52 people per square mile (20 per km²), placing Summit County #1,513 nationally for density and #12 in Colorado. The median county equivalent has 47 people per square mile; the Colorado median is 11. Put another way, there are about 12 acres of land per resident.
| July 1 | 2020 | 2021 | 2022 | 2023 | 2024 | 2025 |
|---|---|---|---|---|---|---|
| Estimate | 31,237 | 31,250 | 31,276 | 31,343 | 31,643 | 31,517 |
| Change | — | +13 | +26 | +67 | +300 | −126 |
U.S. Census Bureau, Vintage 2025 population estimates. Estimates are revised each year and are not decennial census counts. Density divides the whole population by the whole county’s land area, so it describes an average, not how settlement is distributed within the county. Population sources and methods.
Cities and towns in Summit County
7 incorporated places lie at least partly in Summit County. Together they are home to 16,459 people (52.2%); the other 15,058 (47.8%) live outside any incorporated place, in unincorporated communities and rural areas.
The largest is Silverthorne town, with 5,418 residents in the county. The county seat, Breckenridge town, has 5,015 residents. By land, Breckenridge town is the largest at 6.041 mi². Among places with at least 1,000 residents in 2020, Silverthorne town grew fastest since then (+22.8%).
| Incorporated place | Population 2025 | Since 2020 | Land mi² |
|---|---|---|---|
| Silverthorne town | 5,418 | +22.8% | 4.051 |
| Breckenridge townCounty seat | 5,015 | −1.2% | 6.041 |
| Frisco town | 2,792 | −4.5% | 1.668 |
| Keystone town | 1,274 | −2% | 1.826 |
| Dillon town | 1,029 | −3.5% | 1.488 |
| Blue River town | 859 | −1.8% | 2.434 |
| Montezuma town | 72 | −4% | 0.079 |
Population: U.S. Census Bureau Vintage 2025 subcounty estimates, counting only the part of each place inside Summit County. Land: 2026 Census Gazetteer, for the whole place even where it extends into other counties. How communities are listed.
Metropolitan area
Summit County is a central county of the Breckenridge, CO Micropolitan Statistical Area. Its 2 county equivalents have 39,069 residents on 985.2 square miles of land; Summit County accounts for 61.7% of the land and 80.7% of the residents. By combined land it ranks #184 of 542 micropolitan areas, and #330 by population.
| County equivalent | Population 2025 | Land mi² |
|---|---|---|
| Summit County | 31,517 | 608.3 |
| Lake County | 7,552 | 376.9 |
ZIP codes
4 ZIP Code Tabulation Areas have land in Summit County, and each lies mostly inside the county.
80424804358044380498
ZIP Code Tabulation Areas are the Census Bureau’s approximations of USPS ZIP Code service areas, from the 2020 Census relationship files. Post-office-box and single-address ZIP Codes have no tabulation area.
Counties bordering Summit County
Summit County shares a land border with 5 county equivalents. It has more land than 2 of them. The largest neighbor is Park County (2,193.5 mi²) and the smallest is Lake County (376.9 mi²). Together with its neighbors, Summit County forms a block of 7,104.9 mi² of land, of which it holds 8.6%.
| Bordering county equivalent | Land mi² | Size vs. Summit | Compare |
|---|---|---|---|
| Park County | 2,193.5 | 3.6× larger | Compare |
| Grand County | 1,846.6 | 3× larger | Compare |
| Eagle County | 1,684.5 | 2.8× larger | Compare |
| Clear Creek County | 395.1 | 1.5× smaller | Compare |
| Lake County | 376.9 | 1.6× smaller | Compare |
How big is Summit County compared with U.S. states?
Summit County has less land than any of the 50 states. Rhode Island, the smallest state by land area, has 1,033.9 mi², about 1.7 times as much. Colorado’s county land could hold about 170 areas the size of Summit County.
Another way to picture it: the same land area would fill a square about 24.7 miles (39.7 km) on each side. Real county shapes are rarely square, so this is a scale reference rather than a width or driving distance.
State figures are the sums of each state’s county-equivalent land measurements in the same Census release, so states and counties are compared on the same basis. Published state totals can differ slightly because of rounding. Compare all states · Counties bigger than entire states.
What stands out about Summit County?
Summit County has more land than 1,627 of the other 3,221 county equivalents in the dataset.
A median is the middle county-equivalent measurement, not the average of the largest and smallest. All three bars use the same linear scale. Very small areas may appear as a thin sliver; the labels retain their values.
Does including water change its rank?
Using land plus water places Summit County at #1,679 nationally by total area, 84 places farther from the top than its land rank. Other county equivalents gain more area when their water measurements are included.
Its water share is 1.8%, compared with a national county-equivalent median of 1.2% — 0.6 percentage points higher. This describes the statistical geography’s land/water mix, not flood exposure or developable land.
Closest positions in the national land ranking
These entries sit immediately beside Summit County in the national ranking. They can be in different states and are not necessarily geographic neighbors.
| Land rank | County equivalent | Land mi² | Comparison |
|---|---|---|---|
| #1594 | Monroe County, Pennsylvania | 608.4 | Compare |
| #1595 | Summit County, Colorado | 608.3 | This county |
| #1596 | Dubuque County, Iowa | 608.3 | Compare |
Calculated from the same Census release as the area table. Total-area order uses original ALAND + AWATER; water shares and chart labels use published square miles. Calculation details.
Representative coordinates
The Census internal point is 39.620061, -106.133720. It represents a location inside the geography; it is not necessarily the centroid or the address of a courthouse.
Source and precision
U.S. Census Bureau, 2026 Gazetteer Files, Counties. Original ALAND: 1,575,563,230 m²; AWATER: 28,310,935 m². Rankings use ALAND; exact ties use ascending GEOID. Tables preserve Census-published square miles to three decimals, with conversions based on those values.
Common questions
How big is Summit County?
Summit County, Colorado has 608.3 square miles (1,575.6 km²) of land and 10.9 square miles of water, for a total area of 619.3 square miles. It ranks #1595 of 3,222 U.S. county equivalents by land area.
Is Summit County the largest county in Colorado?
No. Summit County ranks #55 of 64 in Colorado by land area. The largest is Las Animas County, with 4,772.9 square miles of land.
What counties border Summit County?
Summit County shares a land border with Eagle County, Grand County, Park County, Clear Creek County, and Lake County.
What is the population of Summit County?
The Census Bureau estimates Summit County had 31,517 residents on July 1, 2025, ranking #1,442 of 3,222 county equivalents. That is 52 people per square mile of land.
What is the county seat of Summit County?
The county seat of Summit County is Breckenridge.
What cities and towns are in Summit County?
Summit County has 7 incorporated places. The most populous five are Silverthorne town, Breckenridge town, Frisco town, Keystone town, and Dillon town; 15,058 residents live outside any incorporated place.
Is Summit County part of a metropolitan area?
Yes. It is a central county of the Breckenridge, CO Micropolitan Statistical Area, which has 2 county equivalents and 39,069 residents.
How many ZIP codes are in Summit County?
4 ZIP Code Tabulation Areas have land in Summit County, and 4 of them have most of their land inside the county. Census ZIP Code Tabulation Areas approximate USPS ZIP Code areas.
How does Summit County compare with U.S. states?
It has less land than every state. Rhode Island, the smallest, has 1.7 times as much land.
How many acres of land are in Summit County?
The land measurement converts to approximately 389,330 acres. Including water, total area is approximately 396,326 acres. One square mile equals 640 acres.
Why might another source show a different area?
Check whether it reports land or total area, its Census vintage, and its rounding. Our guide explains how to reconcile county area figures.
Can this establish a property boundary?
No. Statistical measurements and generalized maps do not establish property lines. Consult the relevant local surveying or land-records authority.