Is Mercer County, NJ a radon risk area?

Mercer County is mapped as Zone 1 - Highest Potential by EPA — meaning the county-wide average indoor level is predicted above 4 pCi/L. Nationally, Mercer County ranks higher in radon potential than 98% of rated counties (the 98th percentile).

Mercer County by the numbers

About 392,138 people live in Mercer County, New Jersey, spread over 224.482 square miles. That works out to roughly 1,747 people per square mile. Rank 57 by population within its EPA zone puts Mercer County at the 95th percentile among zone peers. Geologically, Mercer County is grouped into EPA Region 2 alongside 82 other counties that share its rock and soil setting.

Zone vs. an actual test

Mercer County's predicted average sits above EPA's own action level of 4 pCi/L — the concentration at which EPA recommends fixing a home — versus a national average around 1.3 pCi/L indoors and 0.4 pCi/L outdoors. Some Mercer 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 Mercer County

Nothing about Mercer 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 New Jersey's state radon program

Mercer County's test kit answers today; a Airthings radon monitor keeps answering for Mercer 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

Every figure on this page traces to EPA's own Map of Radon Zones and Census data, documented in the methodology guide. Whatever zone Mercer County carries, the zone explainer covers what it does and doesn't tell you about any one house.