Union Mill is a community in Fairfax County, Virginia, home to about 4,484 people across 10.0 square miles. It has no ZIP code of its own: it’s part of 20124 and 22039.
Homes sold for a median of $305 per square foot across 2 ZIP codes in the three months ending August 2026, and all of them were seller’s markets.
Mostly Centreville; part is in Union Mill
Mostly Fairfax Station; part is in Union Mill
Each card is that ZIP code’s whole market, including any part outside Union Mill. Seller’s market: under 4 months of supply; buyer’s market: over 6. Methodology
We’re writing up Union Mill’s story and what everyday life there is like, for people thinking about moving in.
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| Nearest major airport | Washington Dulles International Airport (IAD)12 miles away |
|---|---|
| Nearest city of 250,000+ | Washington, DC21 miles away |
| Nearest city of 1 million+ | Philadelphia, PA147 miles away |
Straight-line distances from the center of Union Mill; driving is longer.
Source: Airports from OurAirports (scheduled passenger service); city centers and populations from the U.S. Census Bureau.
Source: Members of Congress from the congress-legislators project; districts from the Census Bureau’s relationship files; governor and mayor from Wikidata.
It’s the 210th largest of 669 towns in Virginia by population.
Fairfax County grew from 18,580 residents in 1900 to 1,150,309 in 2020.
Fairfax County, 1900–2020
Source: U.S. Census Bureau decennial censuses (counties 1900–1990 from the Bureau’s historical county file).
Average highs peak around 84°F in summer, and winter lows average 23°F. About 43.5 inches of rain and melted snow fall in a typical year, with about 19 inches of snow.
Source: NOAA 1991–2020 climate normals, Vienna, VA weather station (9 miles away).
696,002 jobs at 31,931 businesses in Fairfax County. The biggest industries by employees:
Source: U.S. Census Bureau County Business Patterns 2023 (private employers; jobs counted where people work).
71 doctors and other health care providers list an office in Union Mill’s ZIP codes.
Nearest hospitals
Providers with an office here
| Primary care doctors | 3 |
|---|---|
| Specialist doctors | 2 |
| Dentists | 6 |
| Nurse practitioners and physician assistants | 15 |
| Mental health providers | 27 |
| Physical and occupational therapists | 15 |
| Optometrists | 2 |
| Chiropractors | 1 |
| Pharmacies | 3 |
Source: Hospitals from CMS Hospital General Information (ratings are CMS overall star ratings); straight-line distances; providers from the CMS National Plan and Provider Enumeration System (NPPES), by practice address and primary specialty.
Parks (3 nearby)
Grocery stores
Pharmacies
Libraries
Museums
Theaters and performance venues
Counts are within about 2.5 miles of the center of town.
Source: Map data © OpenStreetMap contributors (openstreetmap.org/copyright), as mapped by volunteers; it can miss places or include closed ones.
Public schools here are run by Fairfax County Public Schools. Check each district’s attendance zones for a specific address.
| School | Grades | Students | Type | Distance |
|---|---|---|---|---|
| Fairview ElementaryFairfax Station | Pre-K–6 | 751 | Public | 2.8 mi |
| Halley ElementaryFairfax Station | Pre-K–6 | 608 | Public | 7.3 mi |
| Silverbrook ElementaryFairfax Station | Pre-K–6 | 799 | Public | 6.5 mi |
| Union Mill ElementaryClifton | Pre-K–6 | 874 | Public | 3.8 mi |
| Liberty MiddleClifton | 7–8 | 913 | Public | 3.1 mi |
| Centreville HighClifton | 9–12 | 2,347 | Public | 3.9 mi |
| School | Grades | Students | Affiliation | Distance |
|---|---|---|---|---|
| Fairfax Baptist Temple AcademyFairfax Station | Pre-K–12 | 326 | Baptist | 3.8 mi |
| St Andrew the Apostle SchoolClifton | Pre-K–8 | 204 | Roman Catholic | 3.3 mi |
Source: U.S. Department of Education, NCES: Common Core of Data (2024-2025) for public schools; Private School Universe Survey (2023-2024) for private schools. Listed by address; we don’t rate schools.
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Shares ZIP codes with Centreville, Fairfax Station, South Run, Crosspointe, Burke Centre and Clifton.
Town boundaries don’t always match ZIP codes: a ZIP code can cross into neighboring towns, and a town can share a ZIP code with its neighbors. Facts describe the town itself; market figures describe whole ZIP codes.