St. Mary's County, Maryland

St. Mary's County population, land area and income

St. Mary's County had 116,469 residents in the Census Vintage 2024 estimate, on 358.6 square miles of land. It ranks 12th of 24 in Maryland by population and 16th by land area. That works out to 324.8 people per square mile, 3.4 times the US average of 96.3, and in the top quarter nationally.

The median county-equivalent in Maryland has 111,399 residents, about the same as St. Mary's County.

Its SAIPE 2023 median household income of $102,345 is in the top tenth among 3,143 counties with an estimate.

How St. Mary's County's population changed since 2020

St. Mary's County gained 2,463 residents between the July 2020 and July 2024 estimates, a rise of 2.2%. That ranks 11th of 24 in Maryland for growth. The median Maryland county changed by +2.1%, and the state as a whole by +1.4%.

Since the April 2020 estimates base, St. Mary's County recorded 5,931 births and 4,338 deaths, a natural change of +1,593. Net international migration added +747 and net domestic migration, people moving to or from other US counties, came to +262. The largest single component was natural change, which added 1,593 people.

Where St. Mary's County is

The Census internal point of St. Mary's County is at 38.223100, -76.534500. It sits in UTM zone 18N. The map shades Maryland's 24 county-equivalents by population change from 2020 to 2024, darker for faster growth, with St. Mary's County outlined. Dots are towns of 1,000+ people with residents in it.

Towns in St. Mary's County

One incorporated place of 1,000+ people has residents in St. Mary's County, 5,041 people together, or 4% of the county. Each figure counts only the part of the town inside St. Mary's County; towns marked "part" extend into another county. The largest is Leonardtown with 5,041.

Counties bordering St. Mary's County

The Census 2024 county adjacency file lists 6 neighbors for St. Mary's County, including 2 across a state line. The most populous is Charles County, MD, with 174,478 residents. Distances run between Census internal points in a straight line.

• Charles County

  174,478 people

  31 mi WNW

• Calvert County

  94,913 people

  21 mi N

• Dorchester County

  33,138 people

  30 mi ENE

• Somerset County

  25,241 people

  38 mi ESE

• VA

  Westmoreland County, VA

  19,235 people

  17 mi WSW

• VA

  Northumberland County, VA

  12,397 people

  27 mi SSE

Distance to Annapolis and the nearest big city

Annapolis is 52.3 miles N of St. Mary's County's internal point in a straight line. The nearest place of 100,000 or more is Alexandria, VA (population 159,102), 50.8 miles away. The nearest place of 10,000 or more is La Plata, MD (population 11,374), 32.3 miles away.

St. Mary's County FIPS code

The FIPS code of St. Mary's County is 24037: state code 24 for Maryland plus county code 037. Use it as text, with the leading zero, when joining Census, BLS, or CDC county tables. SAIPE lists its 2023 median household income as $102,345.