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 Larimer County, Colorado
EPA puts Larimer County in Zone 1, its highest radon zone, and high results are common there: 49.4% of the 1,902 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
49.4%
10.5 pts above CO
- Larimer
- 49.4%
- Colorado
- 38.9%
1,902 tests, 2023
Median result
3.8pCi/L
Below action level
- Larimer
- 3.8 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2023
Tests reported
1,902
5th of 38 by tests
- Larimer
- 1,902
- 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
9 of 38
Top quarter
- Larimer
- 49.4%
- Park
- 57.5%
By share, of 38 with 30+ tests
Read a result for Larimer County
Starts at Larimer County's median, 3.8 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 3.8 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. Larimer County's median reported result, 2023.
The data
Larimer County, At a glance
Larimer County at a glance
Predicted: EPA radon zone
EPA Zone 1: highest predicted potential
EPA puts all of Larimer 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 Larimer County, 2023
| Year | Share of reported tests at or above 4 pCi/L |
|---|---|
| 2014 | 55.2% |
| 2015 | 62.3% |
| 2016 | 49.8% |
| 2017 | 48.0% |
| 2018 | 51.1% |
| 2019 | 52.0% |
| 2020 | 48.2% |
| 2021 | 57.1% |
| 2022 | 55.4% |
| 2023 | 49.4% |
2023: 49.4%. Across these years the share ran from 48.0% to 62.3%. Each column counts radon tests reported to CDC that year, not homes.
What these figures count
These are the 1,902 tests reported to CDC for Larimer 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).
Larimer County, Compared
Larimer County radon figures, compared
Calculated by Radon411In Larimer County, about 5 in 10 reported tests in 2023 (940 of 1,902) were at or above EPA's action level. Against the national pool of 33.4%, the gap is 16.0 points higher. Across 61 Colorado counties pooled together, 38.9% of tests reached that level, so Larimer County runs 10.5 points above its state.
Of 3 neighbours with a figure, none reported a larger share at or above 4 pCi/L; the spread is 34.2% (Boulder County) to 46.0% (Weld County). By share, Larimer County is 9th of 38 Colorado counties with 30 or more tests for the same period.
Year by year, 2014 opened at 55.2% and 2023 closed at 49.4% (down 5.8 points), with 2015 the high at 62.3%. Half the tests came in under 3.8 pCi/L and half over it; the single highest reached 798.2 pCi/L. Below the action level, 640 tests (33.6%) came in under 2 pCi/L, against 39.2% statewide, and 322 tests (16.9%) fell between 2 and 4, against 22.0% statewide.
Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 49.4% share point the same way here. USGS geology rates 98% of the county's land high radon potential. CDC also counts 442 tests taken after mitigation in Larimer County for the same period: tests in homes where a fix was already in.
The busiest year on file was 2019, with 2,592 tests reported; the quietest, 2014, had 708.
Larimer CountyColorado, pooled
49.4% % of tests38.9% % of tests
| Year | Tests | Larimer County, at or above 4 pCi/L | Colorado, pooled |
|---|---|---|---|
| 2014 | 708 | 55.2% | 46.5% |
| 2015 | 956 | 62.3% | 47.2% |
| 2016 | 1,419 | 49.8% | 38.5% |
| 2017 | 1,283 | 48.0% | 41.0% |
| 2018 | 2,251 | 51.1% | 44.2% |
| 2019 | 2,592 | 52.0% | 44.1% |
| 2020 | 1,821 | 48.2% | 41.9% |
| 2021 | 2,145 | 57.1% | 47.3% |
| 2022 | 1,841 | 55.4% | 38.6% |
| 2023 | 1,902 | 49.4% | 38.9% |
Pooled shares: Radon411's sum of CDC's county counts for one period.
Larimer County, State data
Colorado's own radon test data
MeasuredWhat Colorado's own agencies publish about radon tests in Larimer 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 Larimer 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
54.6%
11,129 of 20,368 tests
Median result
4.6 pCi/L
Highest result
1146.8 pCi/L
Tests behind these figures
20,368 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.
Larimer County, Geology
The ground under Larimer County
PredictedMost of the ground under Larimer County is one class on USGS's geologic map: 98.4% of its land is high radon potential, with 1.6% moderate. The map puts 87.0% of Larimer County in the area it calls Rocky Mountains and 11.4% in High Plains, with one smaller area beside them. USGS gives the first a radon index of 15 and the second 12, both 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 | 87.0% |
| High Plains | Quaternary deposits and Cretaceous marine shales that locally have a high radiometric signature. | High | 12 | 11.4% |
| White River Formation | Siltstone, sandstone, conglomerate, volcanic tuff. | Moderate | 11 | 1.6% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Larimer County beside the ground around it
Larimer County has more high-potential ground than Colorado as a whole: 98.4% of its land against 74.8%. Of the 6 counties that border it, 3 have more high-potential ground, Boulder County the most at 100%.
The map rates the ground, not the air in any home.
Local help
Larimer County, Local resources
Radon testing and mitigation in Larimer County
Listed radon businesses with an address in Larimer 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: Fort Collins
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
Larimer County, Questions
Questions about radon in Larimer County
Are radon levels high in Larimer County?
In 2023, 49.4% of the radon tests reported to CDC for Larimer County, Colorado were at or above 4 pCi/L, and the median reported pre-mitigation result was 3.8 pCi/L. Of 38 Colorado counties with 30 or more tests for the same period, 8 reported a higher share; pooled, the state comes to 38.9%.
Which counties border Larimer County?
Larimer County borders 6 counties: Boulder County, CO, Jackson County, CO, Weld County, CO, Grand County, CO, Laramie County, WY and Albany County, WY.
Products
Larimer County, Products
Testing a home in Larimer County
In Larimer County, 49.4% of 1,902 tests reported to CDC in 2023 reached 4 pCi/L, against 38.9% pooled across Colorado. In Zone 1 the year-round level in Larimer 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
Monitor
RadonScan USB-powered radon monitor with a color screen
- C-NRPP 2024/25: Not included
- Plug-in
- Alarm
- Screen
First reading: Within 5 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
Larimer County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Larimer County
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Larimer County, Bordering counties
Counties bordering Larimer County
Calculated by Radon411- Radon levels in Jackson County, COEPA zone 1
50.0%at or above 4 pCi/L
Median 3.3 pCi/L · 14 tests · 0.6 points above Larimer County
- Radon levels in Weld County, COEPA zone 1
46.0%at or above 4 pCi/L
Median 3.5 pCi/L · 663 tests · 3.4 points below Larimer County
- Radon levels in Grand County, COEPA zone 1
44.1%at or above 4 pCi/L
Median 3.3 pCi/L · 136 tests · 5.3 points below Larimer County
- Radon levels in Boulder County, COEPA zone 1
34.2%at or above 4 pCi/L
Median 2.5 pCi/L · 1,963 tests · 15.2 points below Larimer County
- Radon levels in Laramie County, WYEPA zone 1
No CDC figure for 2023; its page reads it against its own neighbours.
- Radon levels in Albany County, WYEPA zone 1
No CDC figure for 2023; its page reads it against its own neighbours.
Larimer County, Cities and towns
Cities and towns in Larimer County
The Census Bureau estimates 377,292 residents in Larimer County for July 1, 2025, 17,350 more than in 2020 (+4.8%). That works out to 145 people per square mile of land. Its largest town, Fort Collins, has 171,500 residents, 45.5% of the total. CDC's 1,902 reported tests for 2023 work out to 5.0 per 1,000 residents (2025 estimate), close to Colorado's 3.6.
From Fort Collins to Estes Park, CDC publishes no figure by town: each reads Larimer County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Fort Collins | 171,500 | +0.9% | 45.5% |
| Loveland | 81,387 | +6.6% | 21.6% |
| Windsorextends beyond Larimer County | 43,840 | +31.9% | Counted whole |
| Johnstownextends beyond Larimer County | 22,433 | +29.2% | Counted whole |
| Berthoudextends beyond Larimer County | 14,080 | +32.8% | Counted whole |
| Wellington | 12,169 | +9.0% | 3.2% |
| Timnathextends beyond Larimer County | 11,600 | +71.7% | Counted whole |
| Estes Park | 5,780 | −2.1% | 1.5% |
Places in Larimer County with a city page: 1 of 2
8 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). A place that extends beyond Larimer County is counted whole, so it has no share.
Larimer County, Homes
Homes in Larimer County
Of Larimer County's 161,882 homes, 65% are detached houses, against 62% across Colorado; 18% are in buildings of five or more homes. Half of its homes were built before 1993, close to Colorado's 1987: 10% date from before 1960 and 37% from 2000 or later. 64% of occupied homes are lived in by their owner (Colorado: 66%); in the rest a tenant can run a test, but a fix is the landlord's to make.
| Homes | Larimer County | Colorado |
|---|---|---|
| Housing units | 161,882 | 2,545,124 |
| Detached houses | 65% | 62% |
| In buildings of 5 or more | 18% | 22% |
| Mobile homes | 3% | 4% |
| Built before 1960 | 10% | 16% |
| Built since 2000 | 37% | 31% |
| Middle year built | 1993 | 1987 |
| Owner-occupied | 64% | 66% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.