St. Mary's County, Maryland
Located in Maryland, St. Mary's County has a population of 115,126 residents and a median age of 37.2 years, making it the #548 most populous county out of 3,222 nationwide. In terms of economic indicators, the county has a poverty rate of 8.0%. The median home value is $407,600, and the median household income is $119,446, which is 59% above the national median.
Demographics
St. Mary's County has a population of 115,126, making it the #548 most populous county in the US. The median age is 37.2 years, which is 4.4% below the national median.
Population Trend
Rankings →Year-over-Year Population Growth
Age & Sex Distribution
Race & Ethnicity
Nativity
Geographic Mobility (Past Year)
Economy
The median household income in St. Mary's County is $119,446, ranking #56 out of 3,222 counties — 58.9% above the national median. The poverty rate is 8.0% and unemployment stands at 3.4%.
Median Household Income Trend
Rankings →Income Distribution
Industry of Employment
Occupation
Housing
The median home value in St. Mary's County is $407,600 (+44.6% vs national). Renters pay a median of $1,747/mo and the homeownership rate is 73.2%.
Median Home Value Trend
Rankings →Household Type
Education
In St. Mary's County, 36.5% of adults age 25+ hold a bachelor's degree or higher, which is 8.2% above the national average, ranking #404 out of 3,222 counties.
Bachelor's Degree or Higher Trend
Rankings →Health & Wellbeing
Life expectancy in St. Mary's County is 77.0 years. 16.5% of adults report poor or fair health and 5.3% lack health insurance. Data from County Health Rankings (2025).
Life Expectancy Trend
Substance Use
13.1% of adults in St. Mary's County smoke , 35.2% are obese , and 19.6% report excessive drinking. The drug overdose death rate is 35.2 per 100,000.
Adult Smoking Trend
Safety
The homicide rate in St. Mary's County is 3.4 per 100,000 and the suicide rate is 12.6 per 100,000. Motor vehicle deaths occur at a rate of 13.9 per 100,000.
Homicide Rate Trend
Families & Children
10.5% of children in St. Mary's County live in poverty and the infant mortality rate is 5.7 per 1,000 live births. The teen birth rate is 10.8 per 1,000 females age 15–19.
Infant Mortality Trend
Civic & Transportation
Voter turnout in St. Mary's County is 66.9%. The mean commute time is 32.6 min, which is 18.1% above the national average.
Voter Turnout Trend
Mean Commute Time Trend
Rankings →Elections
In the 2024 presidential election, St. Mary's County voted Republican with a margin of 17.2%. The vote was 40.2% Dem / 57.4% Rep. Compared to 2020, the margin shifted 3.4 toward Republicans .
Vote Share Over Time
About St. Mary's County, Maryland
St. Mary's County, Maryland has a total population of 115,126, making it the 548th most populous county in the United States. The median age in St. Mary's County is 37.2 years, which is 4.4% below the national median of 38.9 years.
The median household income in St. Mary's County is $119,446, which ranks #56 of 3,222 counties nationwide. This is 58.9% above the national median of $75,149. The poverty rate is 8.0%, lower than the national rate of 12.6%. The unemployment rate stands at 3.4%.
The median home value in St. Mary's County is $407,600, 44.6% above the national median. Renters in St. Mary's County pay a median gross rent of $1,747 per month. The homeownership rate is 73.2%, compared to the national rate of 64.4%.
In St. Mary's County, 36.5% of residents aged 25 and older hold a bachelor's degree or higher, 8.2% above the national average of 33.7%. Health insurance coverage stands at 96.1% of the population. The average commute time for workers is 32.6 min.
St. Mary's County is a diverse community. The largest racial or ethnic group is White (non-Hispanic) at 70.3% of the population, followed by Black (non-Hispanic) (14.6%) and Hispanic or Latino (6.1%).
All data for St. Mary's County, Maryland comes from the U.S. Census Bureau's American Community Survey (ACS) 5-Year Estimates. These figures are estimates based on survey sampling and are subject to margin of error. For the most detailed and up-to-date data, visit the Census Bureau's official data portal.