Fairfax County area

Population and density of Fairfax County

The Census Bureau estimates that 1,167,873 people lived in Fairfax County on July 1, 2025. That ranks #42 of 3,222 county equivalents nationally and #1 of 133 in Virginia. Since the April 1, 2020 estimates base of 1,150,294, the population has grown by 17,579 (+1.5%), compared with +2.9% for Virginia as a whole.

With 391 square miles of land, that is 2,987 people per square mile (1,153 per km²), placing Fairfax County #43 nationally for density and #12 in Virginia. The median county equivalent has 47 people per square mile; the Virginia median is 109. Put another way, there are about 0.214 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 Fairfax County

3 incorporated places lie at least partly in Fairfax County. Together they are home to 42,438 people (3.6%); the other 1,125,435 (96.4%) live outside any incorporated place, in unincorporated communities and rural areas.

The largest is Herndon town, with 25,506 residents in the county (the city extends into 1 other county). By land, Vienna town is the largest at 4.403 mi². Among places with at least 1,000 residents in 2020, Herndon town grew fastest since then (+3.5%).

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

Metropolitan area

Fairfax County is a central county of the Washington-Arlington-Alexandria, DC-VA-MD-WV Metropolitan Statistical Area, in the Arlington-Alexandria-Reston, VA-WV metropolitan division. Its 23 county equivalents have 6,465,724 residents on 6,033.7 square miles of land; Fairfax County accounts for 6.5% of the land and 18.1% of the residents. By combined land it ranks #35 of 393 metropolitan areas, and #7 by population. It belongs to the Washington-Baltimore-Arlington, DC-MD-VA-WV-PA Combined Statistical Area.

ZIP codes

49 ZIP Code Tabulation Areas have land in Fairfax County; 43 of them have most of their land inside the county, and the others mainly cover neighboring areas.

20120201212012420151201702017120190201912019422003220152202722030220312203222033220352203922041220422204322044220462206022066220792210122102221242215022151221522215322180221812218222203222072230222303223042230622307223082230922310223112231222315

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 Fairfax County

Fairfax County shares a land border with 9 county equivalents, including 3 in Maryland. It has more land than 5 of them. The largest neighbor is Loudoun County (515.7 mi²) and the smallest is Falls Church city (2 mi²). Together with its neighbors, Fairfax County forms a block of 2,724.8 mi² of land, of which it holds 14.4%.

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

Fairfax County has less land than any of the 50 states. Rhode Island, the smallest state by land area, has 1,033.9 mi², about 2.6 times as much. Virginia’s county land could hold about 101 areas the size of Fairfax County.

Another way to picture it: the same land area would fill a square about 19.8 miles (31.8 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 Fairfax County?

Fairfax County has more land than 651 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 Fairfax County at #2,569 nationally by total area, 2 places closer to the top than its land rank. The water assigned to this geography moves it ahead of some county equivalents with more land.

Its water share is 3.8%, compared with a national county-equivalent median of 1.2% — 2.6 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 Fairfax 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.