Is New Castle County, DE a radon risk area?

New Castle County is mapped as Zone 2 - Moderate Potential by EPA — meaning the county-wide average indoor level is predicted between 2 and 4 pCi/L. Nationally, New Castle County ranks higher in radon potential than 65% of rated counties (the 65th percentile).

Where New Castle County sits nationally

About 588,093 people live in New Castle County, Delaware, spread over 426.338 square miles. Averaged across its land area, New Castle County runs about 1,379 people per square mile. Rank 42 by population within its EPA zone puts New Castle County at the 96th percentile among zone peers. New Castle County falls in EPA Radon Region 3, one of 245 counties nationally EPA assigns to that same geologic province.

What this actually means for a house in New Castle County

EPA's Zone 2 rating for New Castle County sits below its own 4 pCi/L action level but above the national indoor average of about 1.3 pCi/L. A county-wide moderate average, like New Castle County's, can still hide a specific house well above or below it — testing is what actually answers the question.

If New Castle County tests above the action level

Nothing about New Castle 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 Delaware's state radon program

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

The methodology guide shows exactly which EPA and Census sources feed New Castle County's numbers. If you're unsure why a low zone still deserves a test, the zone explainer covers that directly.