Is Clayton County, IA a radon risk area?

Clayton County is mapped as Zone 1 - Highest Potential by EPA — meaning the county-wide average indoor level is predicted above 4 pCi/L. Rank it against the rest of the country and Clayton County lands in the 80th percentile for radon potential.

Clayton County by the numbers

About 16,931 people live in Clayton County, Iowa, spread over 778.464 square miles. Averaged across its land area, Clayton County runs about 22 people per square mile. Rank 619 by population within its EPA zone puts Clayton County at the 42nd percentile among zone peers. Clayton County falls in EPA Radon Region 7, one of 412 counties nationally EPA assigns to that same geologic province.

What this actually means for a house in Clayton County

Where the national indoor average runs about 1.3 pCi/L, Clayton 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 Clayton County will test well under the action level, and EPA's guidance is to test regardless of zone.

If Clayton County tests above the action level

Nothing about Clayton 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 Iowa's state radon program

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

Clayton 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.