Radon in Colorado: radon map by county
EPA's Map of Radon Zones puts 53 of Colorado's 64 counties in Zone 1 (predicted average indoor radon above 4 pCi/L), 11 in Zone 2 and 0 in Zone 3. Of 69,620 building tests that radon laboratories reported for 2008 to 2017, 46.6% were at or above EPA's 4 pCi/L action level, against 36.5% nationally (number 7 of 42 states with 1,000+ tests). The highest county share is Kit Carson County (71.4% of 31 tests).
Radon by county in Colorado
| County | EPA zone | Lab tests | Median | 4+ pCi/L |
|---|---|---|---|---|
| Adams County | Zone 1 | 3,872 | 3.0 | 41.4% |
| Alamosa County | Zone 2 | 58 | 2.1 | 26.6% |
| Arapahoe County | Zone 1 | 7,639 | 3.4 | 45.3% |
| Archuleta County | Zone 2 | 297 | 2.3 | 31.2% |
| Baca County | Zone 1 | 23 | 4.8 | 67.7% |
| Bent County | Zone 1 | 27 | 4.2 | 59.4% |
| Boulder County | Zone 1 | 7,468 | 3.4 | 44.8% |
| Broomfield County | Zone 1 | 1,392 | 3.1 | 42.6% |
| Chaffee County | Zone 1 | 340 | 5.1 | 60.4% |
| Cheyenne County | Zone 1 | 3 | 4.9 | 66.7% |
| Clear Creek County | Zone 1 | 92 | 3.5 | 45.8% |
| Conejos County | Zone 2 | 7 | 2.4 | 15.4% |
| Costilla County | Zone 2 | 7 | 3.0 | 36.4% |
| Crowley County | Zone 1 | 2 | 4.8 | 100% |
| Custer County | Zone 1 | 77 | 4.7 | 54.8% |
| Delta County | Zone 1 | 180 | 4.5 | 55.2% |
| Denver County | Zone 1 | 5,972 | 3.3 | 41.8% |
| Dolores County | Zone 1 | 3 | 3.4 | 33.3% |
| Douglas County | Zone 1 | 5,640 | 2.6 | 39% |
| Eagle County | Zone 2 | 329 | 3.5 | 45.8% |
| El Paso County | Zone 1 | 6,655 | 3.2 | 42.1% |
| Elbert County | Zone 1 | 319 | 3.2 | 42.9% |
| Fremont County | Zone 1 | 231 | 5.2 | 58.1% |
| Garfield County | Zone 1 | 1,005 | 3.6 | 46.7% |
| Gilpin County | Zone 1 | 131 | 6.8 | 64.6% |
| Grand County | Zone 1 | 28 | 3.8 | 47.4% |
| Gunnison County | Zone 1 | 198 | 4.1 | 51.6% |
| Hinsdale County | Zone 2 | 6 | 33.4 | 72.7% |
| Huerfano County | Zone 1 | 47 | 4.2 | 53.7% |
| Jackson County | Zone 1 | 3 | 24.8 | 80% |
| Jefferson County | Zone 1 | 8,990 | 3.6 | 46.8% |
| Kiowa County | Zone 1 | 10 | 5.8 | 63.6% |
| Kit Carson County | Zone 1 | 31 | 5.3 | 71.4% |
| La Plata County | Zone 1 | 922 | 3.6 | 46% |
| Lake County | Zone 1 | 133 | 3.3 | 47% |
| Larimer County | Zone 1 | 6,319 | 5.0 | 57.9% |
| Las Animas County | Zone 1 | 133 | 5.4 | 61.9% |
| Lincoln County | Zone 1 | 9 | 4.0 | 50% |
| Logan County | Zone 1 | 57 | 4.8 | 58.8% |
| Mesa County | Zone 1 | 1,655 | 2.9 | 35.8% |
| Mineral County | Zone 2 | 8 | 13.1 | 71.4% |
| Moffat County | Zone 1 | 130 | 4.3 | 55% |
| Montezuma County | Zone 1 | 123 | 3.1 | 37.6% |
| Montrose County | Zone 1 | 752 | 5.1 | 60.7% |
| Morgan County | Zone 1 | 146 | 4.9 | 59.1% |
| Otero County | Zone 1 | 36 | 4.6 | 57.9% |
| Ouray County | Zone 1 | 84 | 4.2 | 53.3% |
| Park County | Zone 1 | 222 | 4.0 | 50.8% |
| Phillips County | Zone 1 | 45 | 3.5 | 40.7% |
| Pitkin County | Zone 1 | 468 | 3.6 | 45.8% |
| Prowers County | Zone 1 | 96 | 3.0 | 31.4% |
| Pueblo County | Zone 1 | 2,202 | 6.2 | 70.1% |
| Rio Blanco County | Zone 1 | 21 | 4.6 | 60% |
| Rio Grande County | Zone 2 | 162 | 3.0 | 37.5% |
| Routt County | Zone 2 | 457 | 3.9 | 49.3% |
| Saguache County | Zone 2 | 14 | 4.2 | 53.8% |
| San Juan County | Zone 2 | n/a | n/a | n/a |
| San Miguel County | Zone 1 | 13 | 4.5 | 52% |
| Sedgwick County | Zone 1 | 12 | 3.8 | 44.4% |
| Summit County | Zone 1 | 254 | 5.0 | 58.7% |
| Teller County | Zone 1 | 675 | 5.2 | 59.6% |
| Washington County | Zone 1 | 60 | 4.6 | 62.8% |
| Weld County | Zone 1 | 3,304 | 3.9 | 49.7% |
| Yuma County | Zone 1 | 26 | 4.0 | 57.1% |
Lab tests: buildings tested by radon laboratories, 2008 to 2017; median in pCi/L; “4+ pCi/L” is the share of tests at or above EPA's action level. n/a: no value on file (no tests, or too few to report).
What the zones mean
Zone 1 counties have a predicted average indoor radon screening level above 4 pCi/L, Zone 2 from 2 to 4 pCi/L and Zone 3 below 2 pCi/L. The prediction is from 1993 indoor measurements, geology, aerial radioactivity, soils and foundation types. EPA: “This map should not be used to determine if individual homes need to be tested.” EPA recommends fixing a home at 4 pCi/L or more and considering a fix between 2 and 4 pCi/L, because there is no known safe level of exposure.
Radon in Colorado: questions
What radon zone is Colorado?
EPA's 1993 map does not give states one zone; it zones each county. In Colorado, 53 counties are Zone 1, 11 Zone 2 and 0 Zone 3. EPA says the map "should not be used to determine if individual homes need to be tested".
Which Colorado counties have the highest radon levels?
By the share of laboratory tests at or above 4 pCi/L for 2008 to 2017 (counties with 20 or more tests): Kit Carson County 71.4% (median 5.3 pCi/L, 31 tests); Pueblo County 70.1% (median 6.2 pCi/L, 2,202 tests); Baca County 67.7% (median 4.8 pCi/L, 23 tests); Gilpin County 64.6% (median 6.8 pCi/L, 131 tests); Washington County 62.8% (median 4.6 pCi/L, 60 tests).
How common is high radon in Colorado?
46.6% of the 69,620 tests in the laboratory data for Colorado (2008 to 2017) were at or above 4 pCi/L; the national share was 36.5%. Buildings are tested by choice, often because of a sale or a concern, so the share describes the tests on file, not every home.
Does Colorado publish its own radon test data?
Colorado's radon program reports county test results; the latest year with county results is 2023, shown on each county page.
Should I test for radon in Colorado?
Yes. EPA recommends testing every home no matter where it is, fixing it at 4 pCi/L or more and considering a fix between 2 and 4 pCi/L, because there is no known safe level of radon exposure.
States bordering Colorado
Other free hazard lookups
- Radon by county and ZIP codeEPA radon zone and the radon test results on file for any county, ZIP code or address.
- Fault lines near an addressUSGS-mapped earthquake faults within 5 miles, their age and slip rate, and the USGS seismic hazard value.
- Power lines near an addressHigh-voltage transmission lines within 1 mile from federal maps, with voltage and distance.
- Flood zone lookupThe FEMA flood zone mapped at any US address. Not an official flood zone determination.
- Superfund sites near an addressThe nearest EPA Superfund (NPL) sites and their status.
All of these, plus wetlands, FEMA hazard ratings and the federal contamination lists, are in the Environmental Records Report for any US address ($29).
Superfund sites in Colorado · Radon map of every state
Data compiled 2026-10-20. County-level screening information, not a radon measurement of any building.