County · code 24037
St. Mary's CountyMaryland
St. Mary's County in Maryland is the state's first county, established in 1637 with its seat in Leonardtown. Named after Mary, the county was created to serve the entire colonial territory.
- Founded1637
- County seatLeonardtown
- Named forMary
- Land area359 sq mi + 406 sq mi water
- Population113,777 2020 Census
- Parcels mapped49,156 checked 15 October 2026
Where it is
St. Mary's on the map of Maryland
Maryland has 24 counties and county equivalents, each with its own records office. Shapes with a page are links.
History
Founded in 1637
An old deed may name a county that no longer exists, or a boundary that has since moved.
St. Mary's County was created on 24 January 1637/1638 as the first county in Maryland, meant to serve the entire colony with estimated boundaries. Over the following decades, the county was renamed Potomac in 1654, then renamed back to St. Mary's in 1658, while losing territory through the creation of Kent, Anne Arundel, and Charles counties. By 1696, the county gained land from Calvert County and has maintained its boundaries since.
- 1638St. Mary's County created By 24 January 1637/1638, St. Marys was created as the first county in Maryland. St. Marys was meant to serve the entire colony; territorial limits, if any, are unknown, and boundaries are estimated. · Archives of Md., 3:60
- 1642Lost territory By 2 August 1642, St. Marys lost to creation of Kent; boundaries are estimated. · Archives of Md., 3:105
- 1650
- 1654Renamed St. Marys renamed Potomac.formerly St. Marys· Archives of Md., 1:341, 345, 347
- c. 1658Renamed Potomac renamed St. Marys.formerly Potomac· Archives of Md., 1:369
Show all 8 changes
- 1638St. Mary's County created By 24 January 1637/1638, St. Marys was created as the first county in Maryland. St. Marys was meant to serve the entire colony; territorial limits, if any, are unknown, and boundaries are estimated. · Archives of Md., 3:60
- 1642Lost territory By 2 August 1642, St. Marys lost to creation of Kent; boundaries are estimated. · Archives of Md., 3:105
- 1650
- 1650Lost territory St. Marys lost to creation of Charles (original, extinct). · Archives of Md., 3:259-260
- 1654Renamed St. Marys renamed Potomac.formerly St. Marys· Archives of Md., 1:341, 345, 347
- c. 1658Renamed Potomac renamed St. Marys.formerly Potomac· Archives of Md., 1:369
- 1658
- 1696
Land and parcels
What the maps cover in St. Mary's
Who publishes each layer, how good it is, and when we last checked.
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Parcels Good enough
Lot lines and tax-map numbers for 49,156 parcels from St. Mary's County. Drawn for tax purposes: usually within a few feet of a survey, but not a survey.
checked 15 October 2026 -
Address points Missing
No public address points layer found for St. Mary's County yet.
-
Buildings Reference
Roof outlines traced from aerial imagery from FEMA Response Geospatial Office with Oak Ridge National Laboratory (ORNL). Good for seeing what is on a lot; not accurate enough to set a fence from.
checked 18 October 2026
- Official
- from the office that keeps the record
- Good enough
- a reliable statewide or national copy
- Fallback
- a guide only; check the official record
- Missing
- nothing public found yet
People and land
St. Mary's by the Census
Source: US Census Bureau, 2020 Census; US Census Bureau, 2020 Gazetteer Files. Not endorsed or certified by the Census Bureau.
Rules and offices
Who to ask before you build, dig or sell
Official county pages only. We link to them; we do not copy them, because they change.
Inside a city or town, permits usually come from that city rather than the county.
Permits
Zoning and code
County government
- County government
The official website of St. Mary's County.
See your own lot on these maps
Open St. Mary's County on Parcel Chart's free map and click your parcel. Save it with a free account; the full record of your place (site map, projects, documents) is Pro, in early access.
Questions
Common questions about St. Mary's County
- When was St. Mary's County founded?
- St. Mary's County was founded in 1637, and named after Mary.
- What is the county seat of St. Mary's County?
- The county seat of St. Mary's County is Leonardtown.
- Is there an online parcel map for St. Mary's County?
- Yes. St. Mary's County publishes a parcel map of 49,156 parcels, rated good enough here. You can click any parcel on it in Parcel Chart's free map, no sign-in needed.
- Has St. Mary's County's boundary or name changed?
- St. Mary's County was created in 1638. Since then the Atlas of Historical County Boundaries records 7 later changes, chiefly involving Charles County, Anne Arundel County and Calvert County. It was formerly called St. Marys and Potomac.
- Who issues building permits in St. Mary's County?
- The county's page on building permits: WIP Phase III MS4 NPDES Permits. Inside a city or town, ask that city first.
- Who issues septic and well permits in St. Mary's County?
- The county's page on septic systems and wells: Health department: septic and well.
- Is my lot in a flood zone?
- We do not have flood maps for St. Mary's County yet. Look up the address on FEMA's Flood Map Service Center, which shows the effective flood map for any lot.
Nearby