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 Grand County, Colorado
EPA puts Grand County in Zone 1, its highest radon zone, and high results are common there: 44.1% of the 136 radon tests reported to CDC (2023) came back 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
44.1%
5.2 pts above CO
- Grand
- 44.1%
- Colorado
- 38.9%
136 tests, 2023
Median result
3.3pCi/L
Below action level
- Grand
- 3.3 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2023
Tests reported
136
23rd of 38 by tests
- Grand
- 136
- 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
16 of 38
Middle half
- Grand
- 44.1%
- Park
- 57.5%
By share, of 38 with 30+ tests
Read a result for Grand County
Starts at Grand County's median, 3.3 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 3.3 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. Grand County's median reported result, 2023.
The data
Grand County, At a glance
Grand County at a glance
Predicted: EPA radon zone
EPA Zone 1: highest predicted potential
EPA puts all of Grand County in
USGS geologic potential: High across 98% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
Radon tests reported for Grand County, 2023
| Year | Share of reported tests at or above 4 pCi/L |
|---|---|
| 2014 | 42.9% |
| 2015 | 45.2% |
| 2016 | 39.6% |
| 2017 | 52.2% |
| 2018 | 46.8% |
| 2019 | 45.1% |
| 2020 | 40.9% |
| 2021 | 45.9% |
| 2022 | 53.8% |
| 2023 | 44.1% |
2023: 44.1%. Across these years the share ran from 39.6% to 53.8%. Each column counts radon tests reported to CDC that year, not homes.
What these figures count
These are the 136 tests reported to CDC for Grand 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).
Grand County, Compared
Grand County radon figures, compared
Calculated by Radon411In Grand County, about 4 in 10 reported tests in 2023 (60 of 136) were at or above EPA's action level. Against the national pool of 33.4%, the gap is 10.7 points higher. Across 61 Colorado counties pooled together, 38.9% of tests reached that level, so Grand County runs 5.2 points above its state.
Of 7 neighbours with a figure, 3 reported a larger share at or above 4 pCi/L and 4 a smaller one; the spread is 26.4% (Gilpin County) to 49.4% (Larimer County). By share, Grand County is 16th of 38 Colorado counties with 30 or more tests for the same period.
Year by year, 2015 opened at 45.2% and 2023 closed at 44.1% (about level), with 2022 the high at 53.8%. Half the tests came in under 3.3 pCi/L and half over it; the single highest reached 67.2 pCi/L. Below the action level, 40 tests (29.4%) came in under 2 pCi/L, against 39.2% statewide, and 36 tests (26.5%) fell between 2 and 4, against 22.0% statewide.
Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 44.1% share point the same way here. USGS geology rates 98% of the county's land high radon potential. CDC also counts 17 tests taken after mitigation in Grand County for the same period: tests in homes where a fix was already in.
The busiest year on file was 2019, with 162 tests reported; the quietest, 2014, had 28.
Grand CountyColorado, pooled
| Year | Tests | Grand County, at or above 4 pCi/L | Colorado, pooled |
|---|---|---|---|
| 2015 | 31 | 45.2% | 47.2% |
| 2016 | 53 | 39.6% | 38.5% |
| 2017 | 46 | 52.2% | 41.0% |
| 2018 | 124 | 46.8% | 44.2% |
| 2019 | 162 | 45.1% | 44.1% |
| 2020 | 137 | 40.9% | 41.9% |
| 2021 | 109 | 45.9% | 47.3% |
| 2022 | 78 | 53.8% | 38.6% |
| 2023 | 136 | 44.1% | 38.9% |
Pooled shares: Radon411's sum of CDC's county counts for one period.
Grand County, State data
Colorado's own radon test data
MeasuredWhat Colorado's own agencies publish about radon tests in Grand 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 Grand 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
43.8%
470 of 1,073 tests
Median result
3.3 pCi/L
Highest result
212.0 pCi/L
Tests behind these figures
1,073 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.
Grand County, Geology
The ground under Grand County
PredictedMost of the ground under Grand County is one class on USGS's geologic map: 98.1% of its land is high radon potential, with 1.9% moderate. 98.1% of it lies in the area the map calls Rocky Mountains, to which USGS gives a radon index of 15, in the high band (12 to 17).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Rocky Mountains | Precambrian granites, gneiss, amphibolite, variable uranium content, abundant shear zones.Sedimentary rocks shed from the granitic highlands. | High | 15 | 98.1% |
| Western Slope | Paleozoic and Mesozoic sandstone, siltstone, shale, basalt. | Moderate | 11 | 1.9% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Grand County beside the ground around it
Grand County has more high-potential ground than Colorado as a whole: 98.1% of its land against 74.8%. Of the 8 counties that border it, 5 have more high-potential ground, Boulder County the most at 100%.
The map rates the ground, not the air in any home.
Local help
Grand County, Local resources
Radon testing and mitigation in Grand 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.
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
Grand County, Questions
Questions about radon in Grand County
Are radon levels high in Grand County?
In 2023, 44.1% of the radon tests reported to CDC for Grand County, Colorado were at or above 4 pCi/L, and the median reported pre-mitigation result was 3.3 pCi/L. Of 38 Colorado counties with 30 or more tests for the same period, 15 reported a higher share; pooled, the state comes to 38.9%.
Which counties border Grand County?
Grand County borders 8 counties: Summit County, Clear Creek County, Gilpin County, Jackson County, Boulder County, Eagle County, Larimer County and Routt County.
Products
Grand County, Products
Testing a home in Grand County
In Grand County, 44.1% of 136 tests reported to CDC in 2023 reached 4 pCi/L, against 38.9% pooled across Colorado. In Zone 1 the year-round level in Grand 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
MonitorAEGTEST
HOUND-1011S rechargeable radon detector with a screen
- C-NRPP 2024/25: Not included
- Battery
- Alarm
- Screen
Method: Semiconductor sensor
First reading: Within 12 hours
Short-term kit
PicoCan short-term charcoal canister radon test
- Lab fee included
Method: Charcoal
In home: 48 to 96 hours
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Grand County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Grand County
Explore
Grand County, Bordering counties
Counties bordering Grand County
Calculated by Radon411- Radon levels in Jackson CountyEPA zone 1
50.0%at or above 4 pCi/L
Median 3.3 pCi/L · 14 tests · 5.9 points above Grand County
- Radon levels in Larimer CountyEPA zone 1
49.4%at or above 4 pCi/L
Median 3.8 pCi/L · 1,902 tests · 5.3 points above Grand County
- Radon levels in Eagle CountyEPA zone 2
45.8%at or above 4 pCi/L
Median 3.5 pCi/L · 312 tests · 1.7 points above Grand County
- Radon levels in Routt CountyEPA zone 2
44.4%at or above 4 pCi/L
Median 3.3 pCi/L · 178 tests · 0.3 points above Grand County
- Radon levels in Clear Creek CountyEPA zone 1
41.2%at or above 4 pCi/L
Median 3.0 pCi/L · 51 tests · 2.9 points below Grand County
- Radon levels in Summit CountyEPA zone 1
38.3%at or above 4 pCi/L
Median 2.0 pCi/L · 295 tests · 5.8 points below Grand County
- Radon levels in Boulder CountyEPA zone 1
34.2%at or above 4 pCi/L
Median 2.5 pCi/L · 1,963 tests · 9.9 points below Grand County
- Radon levels in Gilpin CountyEPA zone 1
26.4%at or above 4 pCi/L
Median 1.1 pCi/L · 129 tests · 17.7 points below Grand County
Grand County, Cities and towns
Cities and towns in Grand County
The Census Bureau estimates 16,496 residents in Grand County for July 1, 2025, 748 more than in 2020 (+4.7%). Spread over its land, that is 8.9 people to the square mile. No town dominates: Granby, the largest, has 2,392 residents, 14.5% of the total. Together its 6 incorporated places hold 46.5% of those residents; the other 53.5% live outside any of them. Testing is reported here more often than across the state: CDC's 136 reported tests for 2023 come to 8.2 for every 1,000 residents (2025 estimate), against 3.6 for Colorado.
From Granby to Grand Lake, CDC publishes no figure by town: each reads Grand County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Granby | 2,392 | +16.5% | 14.5% |
| Fraser | 1,543 | +10.8% | 9.4% |
| Kremmling | 1,451 | −3.9% | 8.8% |
| Winter Park | 1,217 | +13.1% | 7.4% |
| Hot Sulphur Springs | 663 | −3.8% | 4.0% |
| Grand Lake | 402 | −2.0% | 2.4% |
6 incorporated places, 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).
Grand County, Homes
Homes in Grand County
Of Grand County's 17,037 homes, 59% are detached houses, against 62% across Colorado; 22% are in buildings of five or more homes. Half of its homes were built before 1990, close to Colorado's 1987: 7% date from before 1960 and 34% from 2000 or later. Owners live in 76% of the occupied homes (Colorado: 66%), so for most households a test and a fix are their own to order.
| Homes | Grand County | Colorado |
|---|---|---|
| Housing units | 17,037 | 2,545,124 |
| Detached houses | 59% | 62% |
| In buildings of 5 or more | 22% | 22% |
| Mobile homes | 3% | 4% |
| Built before 1960 | 7% | 16% |
| Built since 2000 | 34% | 31% |
| Middle year built | 1990 | 1987 |
| Owner-occupied | 76% | 66% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.