Is Hillsborough County, NH a radon risk area?

EPA places Hillsborough 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. Hillsborough County sits at the 64th percentile nationally for radon potential — above 64 of every 100 rated counties.

Where Hillsborough County sits nationally

About 430,462 people live in Hillsborough County, New Hampshire, spread over 876.53 square miles. Population density there runs about 491 people per square mile. Rank 59 by population within its EPA zone puts Hillsborough County at the 94th percentile among zone peers. Geologically, Hillsborough County is grouped into EPA Region 1 alongside 58 other counties that share its rock and soil setting.

Zone vs. an actual test

Hillsborough County's Zone 2 prediction clears the 1.3 pCi/L national indoor average without reaching EPA's own 4 pCi/L point for recommending a fix. Nothing about a Zone 2 label lowers the case for testing in Hillsborough County — EPA recommends it in every zone, moderate included.

If Hillsborough County tests above the action level

Nothing about Hillsborough 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 Hampshire's state radon program

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

Every figure on this page traces to EPA's own Map of Radon Zones and Census data, documented in the methodology guide. The guide to what a radon zone actually means covers why testing matters in every zone, not just Zone 1.