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ZIP codes in St. Mary's County

29 ZIPs touch St. Mary's County, Maryland. The blue dashed line is the county border; orange ZIPs reach into it.

29

ZIP codes

2

cross the county line

118,665

people in these ZIPs

24

counties in MD

Most people

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St. Mary's County ZIP list

More counties in Maryland

All 24 counties in Maryland

Questions people actually ask

How many ZIP codes are in St. Mary's County, Maryland?

29 ZIP codes reach into St. Mary's County, including 2 PO Box or single-address ZIPs placed by the town they serve. 2 of them are only partly in the county and also cover a neighboring county.

Which ZIP code in St. Mary's County has the most people?

20653 (Lexington Park) has about 26,852 residents, the most of any ZIP touching St. Mary's County, in the Census Bureau’s ACS 2020–2024 estimates.

Can a ZIP code be in St. Mary's County and another county?

Yes. ZIP codes follow mail routes, not county lines. Rows marked with a percentage show how much of that ZIP’s land is in St. Mary's County. For one address, pin the exact spot on the ZIP finder to see its county.

Where does this list come from?

ZIP areas and their county overlaps come from the Census Bureau’s 2020 ZIP Code Tabulation Area to county relationship file. PO Box ZIPs have no area, so each is placed in the county of the ZIP area nearest the town it serves.

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Updated 2026-11-10 · Where the data comes from