Is Larimer County, CO a radon risk area?

Larimer County is mapped as Zone 1 - Highest Potential by EPA — meaning the county-wide average indoor level is predicted above 4 pCi/L. Larimer County sits at the 98th percentile nationally for radon potential — above 98 of every 100 rated counties.

How Larimer County compares

About 374,574 people live in Larimer County, Colorado, spread over 2,595.745 square miles. Averaged across its land area, Larimer County runs about 144 people per square mile. Rank 62 by population within its EPA zone puts Larimer County at the 94th percentile among zone peers. EPA's geology-based Region 8 groups Larimer County with 290 other counties nationally sharing its underlying rock and soil profile.

Why the zone isn't the answer by itself

Larimer County's predicted average sits above EPA's own action level of 4 pCi/L — the concentration at which EPA recommends fixing a home — versus a national average around 1.3 pCi/L indoors and 0.4 pCi/L outdoors. Some Larimer County homes will test comfortably under the action level despite the county's Zone 1 rating — the only way to know which kind of home you have is an actual test.

If Larimer County tests above the action level

Nothing about Larimer 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

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

More on how this number was built

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.