Is Baltimore County, MD a radon risk area?
Baltimore County is mapped as Zone 1 - Highest Potential by EPA — meaning the county-wide average indoor level is predicted above 4 pCi/L. Baltimore County sits at the 100th percentile nationally for radon potential — above 100 of every 100 rated counties.
Where Baltimore County sits nationally
About 852,425 people live in Baltimore County, Maryland, spread over 598.359 square miles. That works out to roughly 1,425 people per square mile. Rank 13 by population within its EPA zone puts Baltimore County at the 99th percentile among zone peers. Baltimore County falls in EPA Radon Region 3, one of 245 counties nationally EPA assigns to that same geologic province.
Why the zone isn't the answer by itself
Where the national indoor average runs about 1.3 pCi/L, Baltimore County's Zone 1 rating puts its predicted county average above EPA's 4 pCi/L action level itself. A Zone 1 rating means testing is worth doing sooner rather than later, but it is still county-wide average, not a reading for any single house — some homes in Baltimore County will test well under the action level, and EPA's guidance is to test regardless of zone.
If Baltimore County tests above the action level
Nothing about Baltimore County's EPA zone changes the mitigation number: $800–$2,500 nationally (around $1,200 typical), set by the house's foundation rather than the county it sits in — and only relevant once a test actually clears 4 pCi/L.
Find Maryland's state radon program
Baltimore County's test kit answers today; a Airthings radon monitor keeps answering for Baltimore 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
Baltimore County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. Whatever zone Baltimore County carries, the zone explainer covers what it does and doesn't tell you about any one house.