Is Jefferson County, IA a radon risk area?

Jefferson County is mapped as Zone 1 - Highest Potential by EPA — meaning the county-wide average indoor level is predicted above 4 pCi/L. Nationally, Jefferson County ranks higher in radon potential than 79% of rated counties (the 79th percentile).

How Jefferson County compares

About 15,781 people live in Jefferson County, Iowa, spread over 435.524 square miles. Population density there runs about 36 people per square mile. Rank 645 by population within its EPA zone puts Jefferson County at the 39th percentile among zone peers. Jefferson 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 Jefferson County

Fixing a home becomes an EPA recommendation past 4 pCi/L, and that is precisely the side of the line Jefferson County's Zone 1 prediction lands on, well above the roughly 1.3 pCi/L most US homes average. Being in Zone 1 raises the odds Jefferson County homes test above the action level, but it does not mean any specific house does — EPA recommends every home be tested, in every zone, because the only way to know is to test.

Testing and mitigation in Jefferson County

Nothing about Jefferson 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

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

Jefferson County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. The guide to what a radon zone actually means covers why testing matters in every zone, not just Zone 1.