Union Mill: Demographics & People
Union Mill is home to 4,484 people, in 1,416 households. Population grew 3.1% from 4,351 (2022) to 4,484 (2024). Median age 47.3 years. (8.7y older than Fairfax County; 9.5y older than Virginia). Children under 18 are 23% of the population. Population is 45% White (non-Hispanic) and 39% Asian. The community is moderately diverse (Simpson index 0.57). 89% of households are family-led. County is losing 28,691 residents per year (2022-2023). County health: 27% adult obesity, 8% smoke.
- 3.2 people per household (vs Virginia avg 2.6).
- 11% non-family households (singles, roommates) (vs Virginia 35%).
- 86 dependents per 100 working-age (youth + seniors / 18-64) (vs Virginia 62).
Population & Trend
Population grew 3.1% from 4,351 (2022) to 4,484 (2024) — about 5.1× the recent U.S. annual rate of ~0.6%/yr. Estimated 2026 population: ~4,622 (extrapolated at 1.5%/yr trend). Census Bureau Vintage estimate: 4,810.
| Census data vintage | 2024 |
|---|---|
| Population | 1,150,309 people |
| Annual growth rate · Population change | 3.1% |
| Annual growth rate · Population (2022) | 4,351 |
| Annual growth rate · Population (2024) | 4,484 |
| Annual growth rate · Population growing | Yes |
| Annual growth rate · Trend category | growing |
| Population | 4,484 people (vs Virginia 42,214) |
| Population Estimate | 4,810 |
Sources: Census ACS 5-Year 2023, Table B01003 · Refreshed 2026-04-12
Age Distribution
Median age 47.3y is 8.4 years older than the U.S. median (38.9y). Children under 18 make up 23% — near the U.S. share of ~22%.
| Age Summary · Median age | 47.3 years (vs Virginia 37.8y) |
|---|---|
| Age Summary · Children Pct | 22.8% |
| Age Summary · Character | established |
| Age Summary · Total Pop | 4,484 |
| Age Summary · Under 18 | 1,021 |
| Age Summary · 18 To 34 | 633.0× |
| Age Summary · 35 To 64 | 1,776.0× |
| Age Summary · 65 Plus | 1,054 |
| Population under 18 | 1,021 |
| Median age | 47.3 years (vs Virginia 37.8y) |
Sources: Census ACS 5-Year 2024 — place-level B01001 query · Census ACS 5-Year 2023 · Refreshed 2026-04-29
Race, Ethnicity & Diversity
Of 4,484 residents, race / ethnicity breaks down by Census ACS counts (a person can identify with one or more groups). The Simpson diversity index is 0.57 (0 = single group, 1 = perfectly even distribution); this is read as moderately diverse.
| White residents | 2,081 |
|---|---|
| Black residents | 39 |
| Asian residents | 1,760 |
| Hispanic or Latino residents | 279 |
| Diversity Index · Diversity index (Simpson) | 56.6% |
| Diversity Index · Diversity label | moderately diverse |
| Diversity Index · Groups counted | 4 |
| Diversity Index · Largest group share | 50.0% |
| Asian population | 39.0% (vs Virginia 5.6%) |
| Black population | 2.0% (vs Virginia 18.2%) |
| Hispanic or Latino population | 6.2% (vs Virginia 10.1%) |
| White (non-Hispanic) population | 45.0% (vs Virginia 53.8%) |
Sources: Census ACS 5-Year 2023 · Refreshed 2026-04-12
Ancestry
Self-reported ancestry from Census ACS — what residents report as their ethnic origin, separate from race. Counts can exceed population because people can list multiple ancestries.
Top (8)
Citizenship & Origin
Where residents were born and their citizenship status (Census ACS). 2.4% are foreign-born — below the U.S. average of 13.9%. 30% have naturalized to U.S. citizenship.
| Residents born in this state | 1,643 |
|---|---|
| Residents born in another state | 1,384 |
| Share born in this state | 36.6% |
| Share born in another state | 63.4% |
| Native-born U.S. citizens | 30.9% |
| Foreign-born residents | 2.4% |
| Naturalized citizens | 30.1% |
| Total foreign-born residents | 1,382 |
| From Europe | 100 |
| From Africa | 1,069 |
| From Latin America | 212 |
Households & Family Composition
1,416 households. Averaging 3.1 people each — larger than the U.S. average of 2.5. 89% are family households — above the U.S. share of ~65%. Of 1,176 families, 32% are married couples with children.
| Children under 18 | 994 |
|---|---|
| Total families | 1,176 |
| Married couples with children | 374 |
| Average household size | 3.14 |
| Women who gave birth (past year) | 2.5% |
| Grandparents living with grandchildren | 151 |
| Grandparents responsible for grandchildren | 63 |
| Family households | 1,261 households (vs Virginia 9,367) |
| Households that are families | 89.1% (vs Virginia 65.0%) |
| Total households | 1,416 households (vs Virginia 14,324) |
Sources: Census ACS 5-Year 2023 · Refreshed 2026-04-12
Residential Stability & Migration
How long residents have lived here and where they came from. 8.9% moved within the county in the past year — the U.S. baseline is roughly 8–10%. The surrounding county is losing 28,691 residents per year on net (IRS migration data).
| Moved within the county (past year) | 8.9% |
|---|---|
| Migration · People moving in (annual) | 1,133,831 |
| Migration · People moving out (annual) | 1,162,522 |
| Migration · Net migration (in − out) | -28,691 |
| Migration · Year | 2022-2023 |
Sources: IRS SOI Migration 2021-2022 · Refreshed 2026-04-12
Disability
Census ACS measures self-reported functional limitations — vision, hearing, mobility, cognitive, self-care, or independent-living. The U.S. baseline disability rate is about 12–13%; rates trend higher with median age.
| Residents with a disability | 111 |
|---|---|
| Disability rate | 2.6% |
Other
| Congressional District · District | 10 |
|---|---|
| Congressional District · Formatted | VA-10 |
| Congressional District · Congress | 118th |
| Cdc Birth Rate · Fips | 51059 |
| Cdc Birth Rate · State Fips | 51 |
| Cdc Birth Rate · County Fips | 059 |
| Cdc Birth Rate · County | Fairfax |
| Cdc Birth Rate · Birth Rate | 8.2% |
| Cdc Birth Rate · Lower Ci | 7.70 |
| Cdc Birth Rate · Upper Ci | 8.70 |
| Cdc Mortality · Fips | 51059 |
| Cdc Mortality · County | Fairfax County |
| Cdc Mortality · Urban Rural | Large fringe metro |
| Cdc Mortality · Total Deaths 2020 2023 | 21,551 |
| Cdc Vaccination · Fips | 51059 |
| Cdc Vaccination · County | Fairfax County |
| Cdc Vaccination · Dose1 Pop Pct | 95.0% |
| Cdc Vaccination · Series Complete Pct | 81.6% |
| Cdc Vaccination · Booster Pct | 49.2% |
| Cdc Vaccination · Population 2019 | 1,147,532 |
| Cdc Vaccination · Metro Status | Metro |
| Family Score · Score | 10 |
| Family Score · Schools | 20 |
| Family Score · Children Pct | 22.8% |
| Family Score · Rating | excellent |
| Town Summary · Key Facts | population 4,484, growing, established, affluent, white collar |
| Town Summary · Population | 4,484 people (vs Virginia 42,214) |
| Town Summary · County | Fairfax County |
Sources: Census place-to-CD118 crosswalk (place_fips) · federal dataset cascade