What EPA's radon map says about Big Horn County

Big Horn County is mapped as Zone 1 - Highest Potential by EPA — meaning the county-wide average indoor level is predicted above 4 pCi/L. Big Horn County sits at the 77th percentile nationally for radon potential — above 77 of every 100 rated counties.

Big Horn County by the numbers

About 12,084 people live in Big Horn County, Wyoming, spread over 3,136.957 square miles. That works out to roughly 4 people per square mile. Among counties sharing Big Horn County's EPA zone, it outranks 33% of them by population. EPA's geology-based Region 8 groups Big Horn County with 290 other counties nationally sharing its underlying rock and soil profile.

Zone vs. an actual test

Where the national indoor average runs about 1.3 pCi/L, Big Horn County's Zone 1 rating puts its predicted county average above EPA's 4 pCi/L action level itself. EPA's guidance doesn't change because of a Zone 1 label: test the house. What changes is the reason to not put it off in Big Horn County specifically.

Next steps for a home in Big Horn County

Mitigation cost doesn't depend on Big Horn County's zone — it depends on the house's foundation. A typical system runs $800–$2,500 (about $1,200 typical), and testing first is what tells you whether that's needed at all.

Find Wyoming's state radon program

Big Horn County's test kit answers today; a Airthings radon monitor keeps answering for Big Horn County over time. Affiliate link, RadonZoneCheck earns a commission there, at no extra cost to you. Use code RADONZONE-10OFF at checkout for 10% off.

More on how this number was built

Big Horn 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.