St. Mary's County: Demographics & People
St. Mary's County's population stands at 115,126 people. Median age 37.2 years. (2.1y younger than Maryland). Population is 15% Black and 6% Hispanic or Latino. County health: 36% adult obesity, 14% smoke.
Population & Trend
Current population 115,126; figures track the most recent Census ACS 5-year estimates.
| Population | 115,126 people |
|---|---|
| Total Town Population | 48,835 people |
Age Distribution
Median age 37.2y is 1.7 years younger than the U.S. median (38.9y).
| Age Summary · Total Pop | 115,126 |
|---|---|
| Age Summary · Under 18 | 27,549 |
| Age Summary · 18 To 34 | 25,993.0× |
| Age Summary · 35 To 64 | 45,440.0× |
| Age Summary · 65 Plus | 16,144 |
| Age Summary · Pct Under 18 | 23.9% |
| Age Summary · Pct 18 To 34 | 22.6% |
| Age Summary · Pct 35 To 64 | 39.5% |
| Median age | 37.2 years (vs Maryland 39.3y) |
Sources: Census ACS 5-Year 2024 — county-level query · Refreshed 2026-04-28
Race, Ethnicity & Diversity
Of 115,126 residents, race / ethnicity breaks down by Census ACS counts (a person can identify with one or more groups).
| Census Demographics · Total Population | 115,126 people |
|---|---|
| White residents | 82,070 |
| Black residents | 16,847 |
| Asian residents | 3,062 |
| Census Demographics · Aian | 130 |
| Census Demographics · Nhpi | 6 |
| Census Demographics · Other Race | 2,366 |
| Census Demographics · Two Or More Races | 10,645 |
| Diversity Index | 46.1% |
| Asian population | 2.7% |
| Black population | 14.6% |
| Hispanic or Latino population | 6.1% |
Sources: Census ACS 5-Year 2024 — county-level query · Refreshed 2026-04-28
Citizenship & Origin
Where residents were born and their citizenship status (Census ACS).
| Census Citizenship · Total | 115,126 |
|---|---|
| Census Citizenship · Native | 110,184 |
| Residents born in this state | 55,689 |
| Residents born in another state | 52,532 |
| Census Citizenship · Foreign Born | 25,148 |
| Census Citizenship · Naturalized | 7,535 |
| Census Citizenship · Non Citizen | 1,963 |
| Foreign-born residents | 21.8% |
Sources: Census ACS 5-Year 2024 — county-level query · Refreshed 2026-04-28
Residential Stability & Migration
How long residents have lived here and where they came from.
| Migration · People moving in (annual) | 112,262 |
|---|---|
| Migration · People moving out (annual) | 112,232 |
| Migration · Net migration (in − out) | 30 |
| Migration · Population growing | Yes |
| Migration · Year | 2022-2023 |
Sources: IRS SOI Migration 2022-2023
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.
| Census Disability · Total Pop | 111,356 |
|---|---|
| With Disability | 13,205 |
| Pct With Disability | 11.9% |
Sources: Census ACS 5-Year 2024 — county-level query · Refreshed 2026-04-28
Group Quarters
Group quarters are non-household living arrangements counted by the Census — college dormitories, nursing homes, military barracks, group homes, correctional facilities, and similar institutional or shared housing. 0 residents live in group quarters.
| Census Group Quarters · Total | 2,674 |
|---|
Sources: Census ACS 5-Year 2024 — county-level query · Refreshed 2026-04-28
Other
| Census Mobility · Total | 113,921 |
|---|---|
| Census Mobility · Same House | 99,768 |
| Census Mobility · Same County | 6,167 |
| Census Mobility · Diff County Same State | 3,108 |
| Census Mobility · Diff State | 4,261 |
| Census Mobility · From Abroad | 617 |
| Census Mobility · Moved Total | 14,153 |
| Census Mobility · Pct Moved In Year | 12.4% |
| Pct White | 71.3% |
Sources: Census ACS 5-Year 2024 — county-level query · Refreshed 2026-04-28