Radon by county
Which Colorado mountain counties have the highest radon?
Radon runs high across Colorado's mountain counties. The county test data shows where the share of high readings sits above the state average.
A live person answers. Not a robot, not a phone tree. Updated September 2026.
Photos: Ski lift climbing the mountain with snowy peaks, morning light, Live Kaiah (Unsplash).
Gilpin and Teller counties lead at 54.9% of radon tests at or above 4 pCi/L, followed by Larimer at 54.6% and Jefferson at 50.3%, per CDPHE data for 2005-2025. Clear Creek is lowest of the ten at 37.3%. The statewide share is 46.4%. CDPHE puts a professional test around $150 and mitigation at $1,000 to $2,000.
Gilpin and Teller.
54.9% of tests at or above 4 pCi/L, 2005-2025.
46.4%.
Share of Colorado tests at or above 4 pCi/L.
Clear Creek, 37.3%.
Still more than 1 in 3 tests.
$150 test.
Mitigation runs $1,000 to $2,000, per CDPHE.
Which mountain counties sit above the state average?
- Gilpin County: 54.9%. Black Hawk and Central City.
- Teller County: 54.9%. Woodland Park.
- Larimer County: 54.6%. Estes Park.
- Jefferson County: 50.3%. Evergreen, Conifer, Golden, Morrison, Indian Hills, Kittredge and Pine.
- Park County: 49.0%. Bailey.
All figures are the share of tests at or above 4 pCi/L, 2005-2025, per CDPHE. The statewide share is 46.4%.
Which mountain counties sit below the state average?
- Summit County: 46.1%. Breckenridge, Frisco, Silverthorne, Dillon and Keystone.
- Eagle County: 44.7%. Vail, Avon and Edwards.
- Grand County: 43.8%. Winter Park and Fraser.
- Boulder County: 43.5%. Nederland, Allenspark and Lyons.
- Clear Creek County: 37.3%. Idaho Springs and Georgetown.
Below average is not low. In every county on this list, more than 1 in 3 tests came in at or above 4 pCi/L.
What do county radon numbers mean for one house?
- A county share is not a house result. Only a test on the house tells you its level.
- The health stakes. CDPHE ties radon to about 500 lung cancer deaths a year in Colorado.
- The action level. The county data counts tests at or above 4 pCi/L.
How should a buyer handle radon on a mountain home?
- Test during inspection. A professional test runs around $150, per CDPHE.
- Price the fix. Mitigation runs $1,000 to $2,000, per CDPHE.
- Ask for past results. Ask the seller for past tests and any mitigation system records.
- Know the disclosure law. SB23-206, in effect since Aug 7, 2023, is a landlord-tenant disclosure, not a home-sale rule.
Call the Kenna Real Estate Group at 303-955-4220 to add a radon test to your inspection.
Questions
Quick answers.
Which Colorado mountain county has the highest radon?
Gilpin and Teller counties, at 54.9% of tests at or above 4 pCi/L from 2005 to 2025, per CDPHE.
What percent of Jefferson County homes test high for radon?
50.3% of tests from 2005 to 2025 came in at or above 4 pCi/L.
Is radon high in Summit County, Colorado?
46.1% of Summit County tests came in at or above 4 pCi/L, close to the statewide 46.4%.
How much does radon mitigation cost in Colorado?
CDPHE puts mitigation at $1,000 to $2,000 and a professional test around $150.
Does a Colorado seller have to disclose radon?
SB23-206 is a landlord-tenant disclosure, not a home-sale rule. Ask the seller for past test results and confirm disclosure duties with a real estate attorney.
Sources
Rules, rates and dates change. The county, town or state office named above has the current version.
Go deeper
Where to go next.
The map
Where the mountain towns are.
Every pin opens that town's page. Drive times from downtown Denver, without traffic.
- Front Range foothills
- I-70 corridor
- Peak to Peak
- Summit County
- Resort
- Tap a town to open its page
Outline: U.S. Census Bureau. Roads from downtown Denver: OSRM on OpenStreetMap. Town points: OpenStreetMap and USGS. Drive times without traffic.
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Colorado Mountain Home Finder is part of the Kenna Real Estate Group at Keller Williams DTC (KWDTC).