County outline
Where St. Mary's County is located
Area breakdown
Land accounts for 46.9% of St. Mary's County’s measured area and water for 53.1%. Its combined area converts to 1,979.4 square kilometers or approximately 489,121 acres.
Green: land · blue: water
| Measurement | Square miles | Square kilometers | Acres |
|---|---|---|---|
| Land | 358.589 | 928.741 | 229,497 |
| Water | 405.663 | 1,050.662 | 259,624.3 |
| Total | 764.252 | 1,979.404 | 489,121.3 |
How St. Mary's County compares
By original Census land area, St. Mary's County ranks #16 of 24 in Maryland and #2660 of 3,222 nationally. National rankings include the 50 states, District of Columbia, and Puerto Rico.
Its land area is 0.857 times the Maryland county-equivalent median of 418.5 square miles. It accounts for 3.7% of the combined county land area in the state.
See the complete Maryland ranking · What counts as a county equivalent?
What stands out about St. Mary's County?
St. Mary's County has more land than 562 of the other 3,221 county equivalents in the dataset.
A median is the middle county-equivalent measurement, not the average of the largest and smallest. All three bars use the same linear scale. Very small areas may appear as a thin sliver; the labels retain their values.
Does including water change its rank?
Using land plus water places St. Mary's County at #1,256 nationally by total area, 1,404 places closer to the top than its land rank. The water assigned to this geography moves it ahead of some county equivalents with more land.
Its water share is 53.1%, compared with a national county-equivalent median of 1.2% — 51.9 percentage points higher. This describes the statistical geography’s land/water mix, not flood exposure or developable land.
Closest positions in the national land ranking
These entries sit immediately beside St. Mary's County in the national ranking. They can be in different states and are not necessarily geographic neighbors.
| Land rank | County equivalent | Land mi² | Comparison |
|---|---|---|---|
| #2659 | McCormick County, South Carolina | 358.9 | Compare |
| #2660 | St. Mary's County, Maryland | 358.6 | This county |
| #2661 | Wetzel County, West Virginia | 358.1 | Compare |
Calculated from the same Census release as the area table. Total-area order uses original ALAND + AWATER; water shares and chart labels use published square miles. Calculation details.
Representative coordinates
The Census internal point is 38.223077, -76.534487. It represents a location inside the geography; it is not necessarily the centroid or the address of a courthouse.
Source and precision
U.S. Census Bureau, 2026 Gazetteer Files, Counties. Original ALAND: 928,740,403 m²; AWATER: 1,050,662,104 m². Rankings use ALAND; exact ties use ascending GEOID. Tables preserve Census-published square miles to three decimals, with conversions based on those values.
Common questions
How many acres of land are in St. Mary's County?
The land measurement converts to approximately 229,497 acres. Including water, total area is approximately 489,121 acres. One square mile equals 640 acres.
Why might another source show a different area?
Check whether it reports land or total area, its Census vintage, and its rounding. Our guide explains how to reconcile county area figures.
Can this establish a property boundary?
No. Statistical measurements and generalized maps do not establish property lines. Consult the relevant local surveying or land-records authority.