What EPA's radon map says about Frederick County

Frederick County is mapped as Zone 1 - Highest Potential by EPA — meaning the county-wide average indoor level is predicted above 4 pCi/L. Frederick County sits at the 98th percentile nationally for radon potential — above 98 of every 100 rated counties.

How Frederick County compares

About 299,317 people live in Frederick County, Maryland, spread over 660.623 square miles. That works out to roughly 453 people per square mile. Among counties sharing Frederick County's EPA zone, it outranks 93% of them by population. Frederick County falls in EPA Radon Region 3, one of 245 counties nationally EPA assigns to that same geologic province.

Zone vs. an actual test

Where the national indoor average runs about 1.3 pCi/L, Frederick County's Zone 1 rating puts its predicted county average above EPA's 4 pCi/L action level itself. Some Frederick County homes will test comfortably under the action level despite the county's Zone 1 rating — the only way to know which kind of home you have is an actual test.

Testing and mitigation in Frederick County

Mitigation cost doesn't depend on Frederick County's zone — it depends on the house's foundation. A typical system runs $800–$2,500 (about $1,200 typical), and testing first is what tells you whether that's needed at all.

Find Maryland's state radon program

Frederick County's test kit answers today; a Airthings radon monitor keeps answering for Frederick County over time. Affiliate link, RadonZoneCheck earns a commission there, at no extra cost to you. RADONZONE-10OFF at checkout knocks 10% off.

More on how this number was built

Frederick County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. Whatever zone Frederick County carries, the zone explainer covers what it does and doesn't tell you about any one house.