Johnson County, WY: EPA's radon zone, explained

EPA's own radon map rates Johnson County zone 1 - highest potential, predicting a county-wide average indoor level above 4 pCi/L. That puts Johnson County in the 74th percentile nationally for radon potential — higher than 74% of the counties EPA has rated.

Where Johnson County sits nationally

Johnson County, Wyoming is home to about 8,803 people across 4,154.152 square miles. Population density there runs about 2 people per square mile. By population, Johnson County is the 801st largest of every county sharing its EPA zone — the 25th percentile by population within that zone. Johnson County falls in EPA Radon Region 8, one of 291 counties nationally EPA assigns to that same geologic province.

Zone vs. an actual test

Fixing a home becomes an EPA recommendation past 4 pCi/L, and that is precisely the side of the line Johnson County's Zone 1 prediction lands on, well above the roughly 1.3 pCi/L most US homes average. That doesn't mean every Johnson County house tests high — a zone is a county-wide prediction, never a single-home reading — but it's a reason to test sooner rather than let it wait.

Next steps for a home in Johnson County

For a Johnson 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 Wyoming's state radon program

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

Where Johnson County's figures come from

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.