Is Denver County, CO a radon risk area?

EPA's own radon map rates Denver County zone 1 - highest potential, predicting a county-wide average indoor level above 4 pCi/L. That puts Denver County in the 99th percentile nationally for radon potential — higher than 99% of the counties EPA has rated.

Where Denver County sits nationally

About 729,019 people live in Denver County, Colorado, spread over 153.074 square miles. Averaged across its land area, Denver County runs about 4,763 people per square mile. Rank 22 by population within its EPA zone puts Denver County at the 98th percentile among zone peers. EPA's geology-based Region 8 groups Denver County with 290 other counties nationally sharing its underlying rock and soil profile.

What this actually means for a house in Denver County

Denver County carries a Zone 1 label because its predicted average clears 4 pCi/L outright — three-plus times the 0.4 pCi/L typical outdoors and above the 1.3 pCi/L most homes see. Being in Zone 1 raises the odds Denver County homes test above the action level, but it does not mean any specific house does — EPA recommends every home be tested, in every zone, because the only way to know is to test.

Testing and mitigation in Denver County

Nothing about Denver 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

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

The methodology guide shows exactly which EPA and Census sources feed Denver County's numbers. Whatever zone Denver County carries, the zone explainer covers what it does and doesn't tell you about any one house.