Arapahoe County area

Population and density of Arapahoe County

The Census Bureau estimates that 673,820 people lived in Arapahoe County on July 1, 2025. That ranks #105 of 3,222 county equivalents nationally and #3 of 64 in Colorado. Since the April 1, 2020 estimates base of 655,085, the population has grown by 18,735 (+2.9%), compared with +4.1% for Colorado as a whole.

With 797.9 square miles of land, that is 845 people per square mile (326 per km²), placing Arapahoe County #220 nationally for density and #3 in Colorado. The median county equivalent has 47 people per square mile; the Colorado median is 11. Put another way, there are about 0.758 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 Arapahoe County

13 incorporated places lie at least partly in Arapahoe County. Together they are home to 569,407 people (84.5%); the other 104,413 (15.5%) live outside any incorporated place, in unincorporated communities and rural areas.

The largest is Aurora city, with 344,658 residents in the county (the city extends into 2 other counties). The county seat, Littleton city, has 43,419 residents. Among places with at least 1,000 residents in 2020, Deer Trail town grew fastest since then (+63.6%).

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

Metropolitan area

Arapahoe 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; Arapahoe County accounts for 9.6% of the land and 21.8% 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

33 ZIP Code Tabulation Areas have land in Arapahoe County; 17 of them have most of their land inside the county, and the others mainly cover neighboring areas.

800108001180012800138001480015800168001780018801028010380105801108011180112801138012080121801228012380128801298013680137802208022280224802308023180236802378024680247

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 Arapahoe County

Arapahoe County shares a land border with 7 county equivalents. It has more land than 2 of them. The largest neighbor is Lincoln County (2,577.7 mi²) and the smallest is Denver County (153.1 mi²). Together with its neighbors, Arapahoe County forms a block of 10,669 mi² of land, of which it holds 7.5%.

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

Arapahoe County has less land than any of the 50 states. Rhode Island, the smallest state by land area, has 1,033.9 mi², about 1.3 times as much. Colorado’s county land could hold about 130 areas the size of Arapahoe County.

Another way to picture it: the same land area would fill a square about 28.2 miles (45.5 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 Arapahoe County?

Arapahoe County has more land than 2,151 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 Arapahoe County at #1,165 nationally by total area, 94 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 0.9%, compared with a national county-equivalent median of 1.2% — 0.2 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 Arapahoe 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.