Douglas County area

Population and density of Douglas County

The Census Bureau estimates that 399,396 people lived in Douglas County on July 1, 2025. That ranks #195 of 3,222 county equivalents nationally and #6 of 64 in Colorado. Since the April 1, 2020 estimates base of 357,993, the population has grown by 41,403 (+11.6%), compared with +4.1% for Colorado as a whole.

With 840.1 square miles of land, that is 475 people per square mile (184 per km²), placing Douglas County #349 nationally for density and #5 in Colorado. The median county equivalent has 47 people per square mile; the Colorado median is 11. Put another way, there are about 1.3 acres of land per resident.

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 Douglas County

7 incorporated places lie at least partly in Douglas County. Together they are home to 185,790 people (46.5%); the other 213,606 (53.5%) live outside any incorporated place, in unincorporated communities and rural areas.

The largest is Castle Rock town, with 83,815 residents in the county. By land, Aurora city is the largest at 164.6 mi² across all its counties. Among places with at least 1,000 residents in 2020, Aurora city grew fastest since then (+70.9%).

Population: U.S. Census Bureau Vintage 2025 subcounty estimates, counting only the part of each place inside Douglas County. Land: 2026 Census Gazetteer, for the whole place even where it extends into other counties. How communities are listed.

Metropolitan area

Douglas County is a central county of the Denver-Aurora-Centennial, CO Metropolitan Statistical Area. Its 10 county equivalents have 3,092,037 residents on 8,344.7 square miles of land; Douglas County accounts for 10.1% of the land and 12.9% of the residents. By combined land it ranks #14 of 393 metropolitan areas, and #19 by population. It belongs to the Denver-Aurora-Greeley, CO Combined Statistical Area.

ZIP codes

18 ZIP Code Tabulation Areas have land in Douglas County; 14 of them have most of their land inside the county, and the others mainly cover neighboring areas.

800168010480106801088010980112801168011880120801248012580126801298013080131801348013580138

ZIP Code Tabulation Areas are the Census Bureau’s approximations of USPS ZIP Code service areas, from the 2020 Census relationship files. Lighter codes have less than half of their land in this county. Post-office-box and single-address ZIP Codes have no tabulation area.

Counties bordering Douglas County

Douglas County shares a land border with 5 county equivalents. It has more land than 3 of them. The largest neighbor is El Paso County (2,126.4 mi²) and the smallest is Teller County (557.1 mi²). Together with its neighbors, Douglas County forms a block of 6,936.8 mi² of land, of which it holds 12.1%.

How big is Douglas County compared with U.S. states?

Douglas County has less land than any of the 50 states. Rhode Island, the smallest state by land area, has 1,033.9 mi², about 1.2 times as much. Colorado’s county land could hold about 123 areas the size of Douglas County.

Another way to picture it: the same land area would fill a square about 29 miles (46.6 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 Douglas County?

Douglas County has more land than 2,228 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 Douglas County at #1,099 nationally by total area, 105 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 0.3%, compared with a national county-equivalent median of 1.2% — 0.9 percentage points lower. 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 Douglas County in the national ranking. They can be in different states and are not necessarily geographic neighbors.

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.