St. Mary's County, MD radon potential

EPA places St. Mary's County in Zone 2 - Moderate Potential — a predicted county-wide average indoor radon level between 2 and 4 pCi/L, based on the geology, soil and aerial radioactivity data behind EPA's national map. St. Mary's County sits at the 60th percentile nationally for radon potential — above 60 of every 100 rated counties.

How St. Mary's County compares

St. Mary's County, Maryland is home to about 116,469 people across 358.589 square miles. That works out to roughly 325 people per square mile. Within its own EPA zone, St. Mary's County is bigger by population than 83% of the counties that share it. St. Mary's County falls in EPA Radon Region 3, one of 245 counties nationally EPA assigns to that same geologic province.

Zone vs. an actual test

Call it a middle case: above the 1.3 pCi/L most US homes average, below the 4 pCi/L line EPA uses to recommend mitigation — that's St. Mary's County's Zone 2 prediction. Middle-of-the-pack doesn't mean risk-free for any one St. Mary's County address — a moderate county average still leaves individual homes to test either side of it.

Next steps for a home in St. Mary's County

A short-term test kit is the standard first step and typically costs far less than mitigation itself. If a test comes back at or above 4 pCi/L, a radon mitigation system for a typical home runs roughly $800–$2,500 (around $1,200 for a common single-family install), driven mainly by foundation type, not by county.

Find Maryland's state radon program

For St. Mary's County, an ongoing number beats a one-time test - a Airthings radon monitor tracks St. Mary's County's levels over time. RadonZoneCheck earns a commission there, at no extra cost to you. Code RADONZONE-10OFF takes 10% off at checkout.

Where St. Mary's County's figures come from

The methodology guide shows exactly which EPA and Census sources feed St. Mary's County's numbers. If you're unsure why a low zone still deserves a test, the zone explainer covers that directly.