Jefferson County, ID: EPA's radon zone, explained

Jefferson 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. Rank it against the rest of the country and Jefferson County lands in the 52nd percentile for radon potential.

Where Jefferson County sits nationally

Jefferson County, Idaho is home to about 34,854 people across 1,093.681 square miles. That works out to roughly 32 people per square mile. By population, Jefferson County is the 442nd largest of every county sharing its EPA zone — the 57th percentile by population within that zone. Jefferson County falls in EPA Radon Region 10, one of 142 counties nationally EPA assigns to that same geologic province.

Why the zone isn't the answer by itself

Call it a middle case: above the 1.3 pCi/L most US homes average, below the 4 pCi/L line EPA uses to recommend mitigation — that's Jefferson County's Zone 2 prediction. Nothing about a Zone 2 label lowers the case for testing in Jefferson County — EPA recommends it in every zone, moderate included.

Next steps for a home in Jefferson County

For a Jefferson County homeowner, the order is simple: test first, since a kit costs a small fraction of what mitigation would. Only if the result clears 4 pCi/L does a system — typically $800–$2,500, about $1,200 for a common install — become worth pricing out.

Find Idaho's state radon program

For Jefferson County, an ongoing number beats a one-time test - a Airthings radon monitor tracks Jefferson County's levels over time. RadonZoneCheck earns a commission there, at no extra cost to you. Code RADONZONE-10OFF takes 10% off at checkout.

Where Jefferson County's figures come from

Jefferson County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. Whatever zone Jefferson County carries, the zone explainer covers what it does and doesn't tell you about any one house.