St. Mary's County, Maryland Demographics
Population trends, housing costs, income, commuting, and health, all on one page.
St. Mary's County, MD Population Density Map and Area Scores
Area Score
Health, income and education, each graded from F to A+. Explore interactive maps for deeper analysis.
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B
Health Around average
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B
Income Around average
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B
Education Around average
Source: Map AI Methodology
Population: density and quick facts
| Metric | St. Mary's County | Maryland Avg | U.S. Average |
|---|---|---|---|
| Population | 115,126 | 6,204,886 | 337,468,954 |
| Population density (per sq mi) | 150.7 | 500.2 | 86.4 |
| Population growth (%/yr) | 0.49% | 0.51% | 0.59% |
| Median age | 38.6 | 38.0 | 37.3 |
| Households | 42,436 | 2,362,551 | 130,235,071 |
Population in St. Mary's County grew by 15.0% from 2009 to 2024, reaching 115,126 in 2024.
Population Growth 2009–2024
Race & Ethnicity
Age & Sex
The largest generation in St. Mary's County is Millennials, aged 29–44, at 22.4% of residents. That is 0.1 points above Maryland as a whole.
- Gen Z 13–28 24,996 21.7% +1.5 pts
- Millennials 29–44 25,816 22.4% +0.1 pts
- Gen X 45–60 24,892 21.6% +0.6 pts
- Boomers 61–79 16,365 14.2% -2.3 pts
Residents by birth cohort, from the 2025 age distribution. The right-hand figure is how far each cohort's share sits above or below Maryland, in percentage points. Children younger than Gen Z and the generations before the Boomers are counted in the population but not shown here, so these shares do not add up to 100%.
Male and female share
Women are 49.6% of the people living in St. Mary's County and men 50.4%.
- Women 49.6% Maryland 51.5%
- Men 50.4% Maryland 48.5%
How many residents match a customer profile?
Residents matching this profile
100% of everyone living in St. Mary's County
Pick an age range and a women/men split and the figure above answers with how many residents that profile reaches.
Economy
St. Mary's County has a the economy index of B, which means it is quite prosperous.
| Metric | St. Mary's County | Maryland Avg | U.S. Average |
|---|---|---|---|
| Median household income | $119,889 | $103,916 | $80,455 |
| Income growth (%/yr) | 4.20% | 3.98% | 4.80% |
| Unemployment rate | 3.4% | 4.8% | 5.2% |
The median household income in St. Mary's County is about 15% higher than in Maryland.
Housing
| Metric | St. Mary's County | Maryland Avg | U.S. Average |
|---|---|---|---|
| Median home price | $350,857 | $267,101 | $248,835 |
| Median rent | $1,747 | $1,704 | $1,407 |
| Homeownership rate | 73.2% | 67.6% | 65.2% |
The median home price in St. Mary's County is about 16.7 years' worth of rent — buying at the median price costs roughly as much as paying the median rent of $1,747 per month for that long.
Commute Time & Mobility
Commuters in St. Mary's County spend about 45 minutes on the road round trip each working day. Over a typical 250-day work year, that adds up to roughly 189 hours, about 7.9 full days, spent commuting.
| Metric | St. Mary's County | Maryland Avg | U.S. Average |
|---|---|---|---|
| One-way commute (min) | 22.7 | 28.3 | 22.4 |
| Round-trip commute (min) | 45.4 | 56.5 | 44.8 |
| Yearly time spent (hours) | 189 | 236 | 187 |
| Estimated yearly cost | $5,868 | $7,301 | $5,790 |
| Work from home | 17.5% | 19.3% | 15.0% |
| Highway traffic (vehicles/day) | 8,343 | 16,437 | 8,813 |
| Local road traffic (vehicles/day) | 1,273 | 2,353 | 1,355 |
Fastest commutes among counties in
Maryland:
Talbot County (17.8 min), Allegany County (17.8 min), Wicomico County (18.1 min).
Slowest:
Charles County (40.0 min), Calvert County (33.6 min), Prince George's County (32.5 min).
The average commute time in St. Mary's County is 23 minutes, shorter than the 28 minutes in Maryland.
Estimated yearly cost applies a single national wage rule of thumb (U.S. Bureau of Labor Statistics average hourly earnings), not a measurement of wages in this area. Traffic volume figures come from proprietary Ticon and TrafficZoom data.
Education & Households
St. Mary's County has a education index of B, which means it is quite educated.
| Metric | St. Mary's County | Maryland Avg | U.S. Average |
|---|---|---|---|
| Bachelor's degree or higher | 32.5% | 39.3% | 31.6% |
| Average household size | 2.65 | 2.57 | 2.53 |
Highest education index among counties in
Maryland:
Howard County (0.5), Montgomery County (0.5), Talbot County (0.4).
Lowest:
Somerset County (0.2), Caroline County (0.2), Allegany County (0.2).
Health
St. Mary's County has a health index of B, which means it is quite healthy.
| Metric | St. Mary's County | Maryland Avg | U.S. Average |
|---|---|---|---|
| Life expectancy (years) | 80.8 | 78.4 | 78.3 |
| Self-rated poor health | 11.5% | 13.2% | 16.3% |
| Smokers | 16.7% | 15.9% | 19.0% |
Highest health index among counties in
Maryland:
Montgomery County (0.8), Howard County (0.8), Frederick County (0.8).
Lowest:
Baltimore city (0.8), Somerset County (0.8), Dorchester County (0.8).
St. Mary's County, MD Compared With Nearby Counties
How St. Mary's County, MD compares with the 2 counties closest to it.
| Area | Population | Median household income | Median home price | Commute |
|---|---|---|---|---|
| St. Mary's County, MD | 115,126 | $119,889 #2/3 | $350,857 #2/3 | 22.7 min #2/3 |
| Calvert County, MD | 94,313 | $134,676 | $403,977 | 33.6 min |
| Dorchester County, MD | 32,754 | $62,608 | $216,435 | 21.6 min |
Frequently Asked Questions
Common questions about St. Mary's County, Maryland.
How many people live in St. Mary's County, Maryland?
About 115,126 people live in St. Mary's County, Maryland, in 42,436 households of 2.7 people on average. The median age is 38.6, close to the U.S. median of 37.3.
Is St. Mary's County, Maryland urban or rural?
Averaged over its land area, St. Mary's County, Maryland has 151 people per square mile, a density typical of a mix of suburbs, small towns and farmland. That is about 1.7 times the U.S. average of 86.
Can a typical household afford a home in St. Mary's County, Maryland?
The median home costs 2.9 times the median household income ($350,857 against $119,889), compared with 3.1 times nationally. That is within the traditional rule of thumb of about 3 times income. Median rent of $1,747 a month takes about 17% of the median household's income, below the 30% level at which HUD considers renters cost-burdened.
Is unemployment high in St. Mary's County, Maryland?
Unemployment in St. Mary's County, Maryland is only 3.4%, well below the U.S. rate of 5.2%, a sign of a tight labor market where employers compete for workers.
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