Adams County area

Population and density of Adams County

The Census Bureau estimates that 554,668 people lived in Adams County on July 1, 2025. That ranks #132 of 3,222 county equivalents nationally and #5 of 64 in Colorado. Since the April 1, 2020 estimates base of 519,580, the population has grown by 35,088 (+6.8%), compared with +4.1% for Colorado as a whole.

With 1,166.8 square miles of land, that is 475 people per square mile (184 per km²), placing Adams County #350 nationally for density and #6 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 Adams County

10 incorporated places lie at least partly in Adams County. Together they are home to 456,154 people (82.2%); the other 98,514 (17.8%) live outside any incorporated place, in unincorporated communities and rural areas.

The largest is Thornton city, with 147,766 residents in the county (the city extends into 1 other county). The county seat, Brighton city, has 44,934 residents. 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, Bennett town grew fastest since then (+54.2%).

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

Metropolitan area

Adams 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; Adams County accounts for 14% of the land and 17.9% 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

35 ZIP Code Tabulation Areas have land in Adams County; 19 of them have most of their land inside the county, and the others mainly cover neighboring areas.

8000280003800108001180019800208002280023800248003080031800458010280103801058013680137802128021680220802218022980233802348023980241802608060180602806038064080642806438065480701

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 Adams County

Adams County shares a land border with 7 county equivalents. It has more land than 4 of them. The largest neighbor is Weld County (3,985 mi²) and the smallest is Broomfield County (33 mi²). Together with its neighbors, Adams County forms a block of 10,698.7 mi² of land, of which it holds 10.9%.

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

Adams County has more land than 1 of the 50 states. It is about 1.1 times the land area of Rhode Island (1,033.9 mi²), while Delaware, the next larger state, has 1.7 times as much land (1,948.6 mi²). Colorado’s county land could hold about 89 areas the size of Adams County.

Another way to picture it: the same land area would fill a square about 34.2 miles (55 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 Adams County?

Adams County has more land than 2,695 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 Adams County at #600 nationally by total area, 73 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 1.4%, compared with a national county-equivalent median of 1.2% — 0.3 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 Adams 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.