Is Custer County, CO a radon risk area?

Custer County is mapped as Zone 1 - Highest Potential by EPA — meaning the county-wide average indoor level is predicted above 4 pCi/L. That puts Custer County in the 71st percentile nationally for radon potential — higher than 71% of the counties EPA has rated.

Custer County by the numbers

About 5,553 people live in Custer County, Colorado, spread over 738.626 square miles. That works out to roughly 8 people per square mile. Rank 905 by population within its EPA zone puts Custer County at the 15th percentile among zone peers. EPA's geology-based Region 8 groups Custer County with 290 other counties nationally sharing its underlying rock and soil profile.

Why the zone isn't the answer by itself

Outdoor air nationally averages about 0.4 pCi/L, indoor air about 1.3 pCi/L — Custer County's Zone 1 prediction clears both of those and EPA's fix-it threshold besides. 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 Custer County specifically.

Testing and mitigation in Custer County

Nothing about Custer 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 Colorado's state radon program

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

Custer 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.