How many people live in St. Mary's County, MD?
Updated Apr. 6, 2026Refreshed annually
In 2024, there were about 116,500 people living in St. Mary's County, MD. That makes St. Mary's County the 12th-most populous county in Maryland. It is home to 1.9% of people living in the state.
116K
population of St. Mary's County, MD (2024)
1.9%
County share of the Maryland population (2024)
About 116,500 people lived in St. Mary's County, MD in 2024.
Population estimates, 2000–2024
What are St. Mary's County, MD’s age demographics?
About 17,600 St. Mary's County, MD residents are aged 65 and older in 2024. That represents 15.1% of its population. For comparison, the age group represents 17.7% of Maryland’s population and 18% in the US overall.
Another 27,600 St. Mary's County residents, or 23.7% of the population, were children under 18. For comparison, the age group represents 22% of Maryland’s population and 21.6% in the US overall.
A lower share of St. Mary's County, MD's population is aged 65 or older than the US as a whole.
Population estimates by age group, (2024)
What are St. Mary's County, MD’s racial and ethnic demographics?
Non-Hispanic white residents make up 70.7% of the St. Mary's County, MD population, higher than the national share of 57.5%. St. Mary's County, MD also has a larger share of people identifying as non-Hispanic Black or African American (15.6%) than the US overall (12.6%).
In contrast, St. Mary's County’s Hispanic population accounts for 6.6%, below the 20% nationwide, and the non-Hispanic Asian population makes up 3% of the county, compared with 6.5% nationally.
Racial and ethnic make up differ based on location. These figures reflect how people identified their race alone (not in combination with other races), and separate out Hispanic or Latino ethnicity, following Census reporting standards.
St. Mary's County, MD has a higher share of a non-Hispanic white population than Maryland as a whole.
Population estimates by race and ethnicity, (2024)
The largest city or town in St. Mary's County, MD is Leonardtown with about 5,000 residents in 2024.
Cities and towns in St. Mary's County, MD ranked by population
Population (2024), includes only portions within county
| City or town | Population | |
|---|---|---|
| 1. | Leonardtown | 5,041 |
| 2. | Balance of St. Mary's County | 111,428 |
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Methodology
USAFacts standardizes data, in areas such as time and demographics, to make it easier to understand and compare.
The analysis was generated with the help of AI and reviewed by USAFacts for accuracy.
Page sources
USAFacts endeavors to share the most up-to-date information available. We sourced the data on this page directly from government agencies; however, the intervals at which agencies publish updated data vary.
