Is Montgomery County, MD a radon risk area?

EPA's own radon map rates Montgomery County zone 1 - highest potential, predicting a county-wide average indoor level above 4 pCi/L. Nationally that's the 100th percentile for radon potential — Montgomery County outranks 100% of every county EPA has rated.

How Montgomery County compares

About 1,082,273 people live in Montgomery County, Maryland, spread over 493.142 square miles. Population density there runs about 2,195 people per square mile. Rank 7 by population within its EPA zone puts Montgomery County at the 99th percentile among zone peers. EPA's geology-based Region 3 groups Montgomery County with 244 other counties nationally sharing its underlying rock and soil profile.

Zone vs. an actual test

Outdoor air nationally averages about 0.4 pCi/L, indoor air about 1.3 pCi/L — Montgomery County's Zone 1 prediction clears both of those and EPA's fix-it threshold besides. That doesn't mean every Montgomery County house tests high — a zone is a county-wide prediction, never a single-home reading — but it's a reason to test sooner rather than let it wait.

If Montgomery County tests above the action level

Nothing about Montgomery 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

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

More on how this number was built

Montgomery County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. If you're unsure why a low zone still deserves a test, the zone explainer covers that directly.