Long-term kit
RL116 long-term radon test kit
- Lab fee extra
Method: Alpha track
In home: 90 days to 12 months
Locations and reports
Radon Levels in Denver County, Colorado
EPA puts Denver County in Zone 1, its highest radon zone, and 35.4% of its 2,277 reported radon tests (2023) were at or above 4 pCi/L. Homes with elevated levels occur in all three zones, so only a test measures yours.
Data checked By Radon411Methodology
Share at 4+ pCi/L
35.4%
3.5 pts below CO
- Denver
- 35.4%
- Colorado
- 38.9%
2,277 tests, 2023
Median result
2.8pCi/L
Below action level
- Denver
- 2.8 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2023
Tests reported
2,277
2nd of 38 by tests
- Denver
- 2,277
- Jefferson
- 3,068
Reported to CDC before any fix, 2023
EPA radon zone
Zone 1
Highest potential
- Zone 1
- 2
- 3
1 highest, 3 lowest
EPA predicts over 4 pCi/L indoors
Rank in Colorado
29 of 38
Middle half
- Denver
- 35.4%
- Park
- 57.5%
By share, of 38 with 30+ tests
Read a result for Denver County
Starts at Denver County's median, 2.8 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 2.8 pCi/L
Between 2 and 4 pCi/L
- Under 20 to 1.9 pCi/L
- 2 to 4consider a fix
- 4 and aboveEPA says fix it
This result is between 2 and 4 pCi/L. EPA recommends considering a fix when the level is between 2 and 4 pCi/L. Denver County's median reported result, 2023.
The data
Denver County, At a glance
Denver County at a glance
Predicted: EPA radon zone
EPA Zone 1: highest predicted potential
EPA puts all of Denver County in
USGS geologic potential: High across 100% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
Radon tests reported for Denver County, 2023
| Year | Share of reported tests at or above 4 pCi/L |
|---|---|
| 2014 | 41.3% |
| 2015 | 41.4% |
| 2016 | 31.4% |
| 2017 | 38.8% |
| 2018 | 38.3% |
| 2019 | 37.2% |
| 2020 | 37.5% |
| 2021 | 43.0% |
| 2022 | 23.6% |
| 2023 | 35.4% |
2023: 35.4%. Across these years the share ran from 23.6% to 43.0%. Each column counts radon tests reported to CDC that year, not homes.
What these figures count
These are the 2,277 tests reported to CDC for Denver County over 2023, many from homes being sold or already suspected of a problem: they describe the county's reported tests, not this house.
Measured: CDC tracking data. Figure above: 2023. Measured data period: 2005 to 2023 (every CDC figure on file).
Denver County, Compared
Denver County radon figures, compared
Calculated by Radon411In Denver County, about 4 in 10 reported tests in 2023 (807 of 2,277) were at or above EPA's action level. Against the national pool of 33.4%, the gap is 2.0 points higher. Across 61 Colorado counties pooled together, 38.9% of tests reached that level, so Denver County runs 3.5 points below its state.
Of 3 neighbours with a figure, all 3 reported a larger share at or above 4 pCi/L; the spread is 36.6% (Adams County) to 41.8% (Jefferson County). By share, Denver County is 29th of 38 Colorado counties with 30 or more tests for the same period.
Year by year, 2014 opened at 41.3% and 2023 closed at 35.4% (down 5.9 points), with 2021 the high at 43.0%. Half the tests came in under 2.8 pCi/L and half over it; the single highest reached 41.5 pCi/L. Below the action level, 862 tests (37.9%) came in under 2 pCi/L, against 39.2% statewide, and 608 tests (26.7%) fell between 2 and 4, against 22.0% statewide.
Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 35.4% share point the same way here. USGS geology rates 100% of the county's land high radon potential. CDC also counts 455 tests taken after mitigation in Denver County for the same period: tests in homes where a fix was already in.
The busiest year on file was 2022, with 3,708 tests reported; the quietest, 2014, had 620.
Denver CountyColorado, pooled
| Year | Tests | Denver County, at or above 4 pCi/L | Colorado, pooled |
|---|---|---|---|
| 2014 | 620 | 41.3% | 46.5% |
| 2015 | 780 | 41.4% | 47.2% |
| 2016 | 1,180 | 31.4% | 38.5% |
| 2017 | 1,099 | 38.8% | 41.0% |
| 2018 | 2,877 | 38.3% | 44.2% |
| 2019 | 2,839 | 37.2% | 44.1% |
| 2020 | 2,338 | 37.5% | 41.9% |
| 2021 | 3,669 | 43.0% | 47.3% |
| 2022 | 3,708 | 23.6% | 38.6% |
| 2023 | 2,277 | 35.4% | 38.9% |
Pooled shares: Radon411's sum of CDC's county counts for one period.
Denver County, State data
Colorado's own radon test data
MeasuredWhat Colorado's own agencies publish about radon tests in Denver County, with their period. These are not CDC's figures and are never added to them.
MeasuredState figures, not CDC's
What Colorado CDPHE reports for Denver County
Radon data (county results): radon test results received from radon testing labs, primarily short-term household tests taken by the homeowner. Period: 2005-2025.
Share over 4 pCi/L
39.8%
8,752 of 21,979 tests
Median result
3.1 pCi/L
Highest result
310.1 pCi/L
Tests behind these figures
21,979 tests
- CDPHE says these data do not give actual radon levels in homes that have not been tested.
- When possible, only tests conducted before a mitigation system was installed are used.
- Some counties have very small numbers of test results, and their summaries may be less representative.
- These figures describe tests reported to Colorado CDPHE in this area. They count a different set of tests than CDC's figures and are not a reading of any one home.
Measured: Colorado CDPHE data, 2005-2025.
Denver County, Geology
The ground under Denver County
PredictedUSGS's geologic map puts all of Denver County's mapped land in one class: high radon potential. The map puts 75.8% of Denver County in the area it calls High Plains and 24.2% in Dawson Arkose. USGS gives the first a radon index of 12 and the second 14, both in the high band (12 to 17).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| High Plains | Quaternary deposits and Cretaceous marine shales that locally have a high radiometric signature. | High | 12 | 75.8% |
| Dawson Arkose | Consolidated alluvial fan and river deposits sourced in the granite mountains to the west. | High | 14 | 24.2% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Denver County beside the ground around it
Denver County has more high-potential ground than Colorado as a whole: 100% of its land against 74.8%. Of the 3 counties that border it, none has as large a share of high-potential ground; Adams County comes nearest at 100%.
The map rates the ground, not the air in any home.
Local help
Denver County, Local resources
Radon testing and mitigation in Denver County
Listed radon businesses with an address in Denver County:
- Colorado's radon programColorado Department of Public Health and EnvironmentColorado's radon program licenses or certifies radon professionals, offers free or discounted test kits and states the rule for disclosing radon when a home is sold, and answers questions about testing and mitigation in Colorado.Visit the program’s page(opens in a new tab)
- Free and low-cost kitsThe program says:
Order a discounted radon test kit
- Compare kits
- Professionals in Colorado25 professionals are listed in Colorado.
Listed radon professionals by town: Denver
What Colorado's program says
- Licensing of radon professionals
Listed contractors are certified by the National Radon Proficiency Program or the National Radon Safety Board, and must be licensed by the Colorado Department of Regulatory Agencies.
- Disclosure when a home is sold or rented
As of August 7, 2023, landlords in Colorado are required to disclose radon information when a tenant signs a lease agreement.
What it means
Denver County, Questions
Questions about radon in Denver County
Are radon levels high in Denver County?
In 2023, 35.4% of the radon tests reported to CDC for Denver County, Colorado were at or above 4 pCi/L, and the median reported pre-mitigation result was 2.8 pCi/L. Of 38 Colorado counties with 30 or more tests for the same period, 28 reported a higher share; pooled, the state comes to 38.9%.
Which counties border Denver County?
Denver County borders 3 counties: Jefferson County, Arapahoe County and Adams County.
Products
Denver County, Products
Testing a home in Denver County
In Denver County, 35.4% of 2,277 tests reported to CDC in 2023 reached 4 pCi/L, against 38.9% pooled across Colorado. In Zone 1 the year-round level in Denver County is the one to know: a long-term test (more than 90 days) or a monitor, with a short-term kit for a first answer.
Test kits and monitors3
See every kit and monitor
MonitorAranet
Radon One battery digital radon monitor with an e-ink screen
- C-NRPP 2024/25: Not included
- Battery
- Bluetooth
- Alarm
- Screen, app
Method: Ion chamber
First reading: Within 10 minutes
Short-term kitKidde
442020 short-term charcoal radon test kit
- Lab fee included
Method: Charcoal
In home: 3 days
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Denver County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Denver County
Explore
Denver County, Bordering counties
Counties bordering Denver County
Calculated by Radon411- Radon levels in Jefferson CountyEPA zone 1
41.8%at or above 4 pCi/L
Median 3.2 pCi/L · 3,068 tests · 6.4 points above Denver County
- Radon levels in Arapahoe CountyEPA zone 1
37.9%at or above 4 pCi/L
Median 2.5 pCi/L · 1,990 tests · 2.5 points above Denver County
- Radon levels in Adams CountyEPA zone 1
36.6%at or above 4 pCi/L
Median 2.3 pCi/L · 1,191 tests · 1.2 points above Denver County
Denver County, Cities and towns
Cities and towns in Denver County
The Census Bureau estimates 740,613 residents in Denver County for July 1, 2025, 22,933 more than in 2020 (+3.2%). Packed into its land, that is 4,838 people per square mile. Denver, its one incorporated place, has 740,613 residents, 100.0% of the total. CDC's 2,277 reported tests for 2023 work out to 3.1 per 1,000 residents (2025 estimate), close to Colorado's 3.6.
Denver is the one incorporated place here; CDC publishes no figure by town, so it reads Denver County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Denver | 740,613 | +3.2% | 100.0% |
One incorporated place, as listed in the U.S. Census Bureau’s 2020 place reference files. Residents: U.S. Census Bureau population estimates for July 1, 2025 (Vintage 2025).
Denver County, Homes
Homes in Denver County
Denver County has 352,593 homes, and many share a building: 45% are in buildings of five or more, 41% are detached houses, against 62% across Colorado. The homes are older than Colorado's as a whole: half were built before 1974 (1987 for Colorado), and 35% date from before 1960. Most occupied homes here are rented: owners live in 49% (Colorado: 66%). A tenant can run a test; a fix is the landlord's to make.
| Homes | Denver County | Colorado |
|---|---|---|
| Housing units | 352,593 | 2,545,124 |
| Detached houses | 41% | 62% |
| In buildings of 5 or more | 45% | 22% |
| Mobile homes | under 1% | 4% |
| Built before 1960 | 35% | 16% |
| Built since 2000 | 29% | 31% |
| Middle year built | 1974 | 1987 |
| Owner-occupied | 49% | 66% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.