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 Custer County, Colorado
EPA puts Custer County in Zone 1, its highest radon zone, and high results are common there: 45.7% of the 35 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
45.7%
6.8 pts above CO
- Custer
- 45.7%
- Colorado
- 38.9%
35 tests, 2023
Median result
3.5pCi/L
Below action level
- Custer
- 3.5 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2023
Tests reported
35
38th of 38 by tests
- Custer
- 35
- 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
13 of 38
Middle half
- Custer
- 45.7%
- Park
- 57.5%
By share, of 38 with 30+ tests
Read a result for Custer County
Starts at Custer County's median, 3.5 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 3.5 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. Custer County's median reported result, 2023.
The data
Custer County, At a glance
Custer County at a glance
Predicted: EPA radon zone
EPA Zone 1: highest predicted potential
EPA puts all of Custer 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 Custer County, 2023
| Year | Share of reported tests at or above 4 pCi/L |
|---|---|
| 2014 | 57.1% |
| 2015 | 50.0% |
| 2016 | 50.0% |
| 2017 | 58.6% |
| 2018 | 47.5% |
| 2019 | 42.3% |
| 2020 | 34.6% |
| 2021 | 41.4% |
| 2022 | 34.8% |
| 2023 | 45.7% |
2023: 45.7%. Across these years the share ran from 34.6% to 58.6%. Each column counts radon tests reported to CDC that year, not homes.
What these figures count
These are the 35 tests reported to CDC for Custer 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).
Custer County, Compared
Custer County radon figures, compared
Calculated by Radon411In Custer County, about 5 in 10 reported tests in 2023 (16 of 35) were at or above EPA's action level. Against the national pool of 33.4%, the gap is 12.3 points higher. Across 61 Colorado counties pooled together, 38.9% of tests reached that level, so Custer County runs 6.8 points above its state.
Of 3 neighbours with a figure, 1 reported a larger share at or above 4 pCi/L and 2 a smaller one; the spread is 28.3% (Huerfano County) to 50.0% (Fremont County). By share, Custer County is 13th of 38 Colorado counties with 30 or more tests for the same period.
Year by year, 2018 opened at 47.5% and 2023 closed at 45.7% (about level), with 2018 the high at 47.5%. Half the tests came in under 3.5 pCi/L and half over it; the single highest reached 217.6 pCi/L. Below the action level, 11 tests (31.4%) came in under 2 pCi/L, against 39.2% statewide, and 8 tests (22.9%) fell between 2 and 4, against 22.0% statewide.
Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 45.7% share point the same way here. USGS geology rates 100% of the county's land high radon potential. CDC also counts 6 tests taken after mitigation in Custer County for the same period: tests in homes where a fix was already in.
The busiest year on file was 2020, with 52 tests reported; the quietest, 2015, had 6.
Custer CountyColorado, pooled
| Year | Tests | Custer County, at or above 4 pCi/L | Colorado, pooled |
|---|---|---|---|
| 2018 | 40 | 47.5% | 44.2% |
| 2020 | 52 | 34.6% | 41.9% |
| 2023 | 35 | 45.7% | 38.9% |
Pooled shares: Radon411's sum of CDC's county counts for one period.
Custer County, State data
Colorado's own radon test data
MeasuredWhat Colorado's own agencies publish about radon tests in Custer 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 Custer 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
44.3%
194 of 438 tests
Median result
3.3 pCi/L
Highest result
217.6 pCi/L
Tests behind these figures
438 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.
Custer County, Geology
The ground under Custer County
PredictedUSGS's geologic map puts all of Custer County's mapped land in one class: high radon potential. 98.4% 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 | 98.4% |
| High Plains | Quaternary deposits and Cretaceous marine shales that locally have a high radiometric signature. | High | 12 | 1.6% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Custer County beside the ground around it
Custer County has more high-potential ground than Colorado as a whole: 100% of its land against 74.8%. Of the 4 counties that border it, none has as large a share of high-potential ground; Fremont County comes nearest at 100%.
The map rates the ground, not the air in any home.
Local help
Custer County, Local resources
Radon testing and mitigation in Custer 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
Custer County, Questions
Questions about radon in Custer County
Are radon levels high in Custer County?
In 2023, 45.7% of the radon tests reported to CDC for Custer County, Colorado were at or above 4 pCi/L, and the median reported pre-mitigation result was 3.5 pCi/L. Of 38 Colorado counties with 30 or more tests for the same period, 12 reported a higher share; pooled, the state comes to 38.9%.
Which counties border Custer County?
Custer County borders 4 counties: Fremont County, Huerfano County, Pueblo County and Saguache County.
Products
Custer County, Products
Testing a home in Custer County
In Custer County, 45.7% of 35 tests reported to CDC in 2023 reached 4 pCi/L, against 38.9% pooled across Colorado. In Zone 1 the year-round level in Custer 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
View Plus radon and air quality monitor
- C-NRPP 2024/25: Approved
- Battery
- Wi-Fi, Bluetooth
- Screen, app
Method: Alpha spectrometry
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
Custer County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Custer County
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Custer County, Bordering counties
Counties bordering Custer County
Calculated by Radon411- Radon levels in Fremont CountyEPA zone 1
50.0%at or above 4 pCi/L
Median 4.0 pCi/L · 66 tests · 4.3 points above Custer County
- Radon levels in Pueblo CountyEPA zone 1
44.4%at or above 4 pCi/L
Median 3.5 pCi/L · 342 tests · 1.3 points below Custer County
- Radon levels in Saguache CountyEPA zone 2
41.7%at or above 4 pCi/L
Median 3.1 pCi/L · 12 tests · 4.0 points below Custer County
- Radon levels in Huerfano CountyEPA zone 1
28.3%at or above 4 pCi/L
Median 1.3 pCi/L · 53 tests · 17.4 points below Custer County
Custer County, Cities and towns
Cities and towns in Custer County
Custer County is growing: the Census Bureau puts it at 5,590 residents on July 1, 2025, up 18.3% from 4,724 in 2020. Spread over its land, that is 7.6 people to the square mile. No town dominates: Silver Cliff, the largest, has 713 residents, 12.8% of the total. Together its 2 incorporated places hold 21.5% of those residents; the other 78.5% live outside any of them. Testing is reported here more often than across the state: CDC's 35 reported tests for 2023 come to 6.3 for every 1,000 residents (2025 estimate), against 3.6 for Colorado.
From Silver Cliff to Westcliffe, CDC publishes no figure by town: each reads Custer County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Silver Cliff | 713 | +15.6% | 12.8% |
| Westcliffe | 488 | +15.4% | 8.7% |
2 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).
Custer County, Homes
Homes in Custer County
Custer County is a place of houses on their own lots: 88% of its 4,349 homes are detached single-family houses, against 62% across Colorado. Half of its homes were built before 1990, close to Colorado's 1987: 17% date from before 1960 and 34% from 2000 or later. Owners live in 86% of the occupied homes (Colorado: 66%), so for most households a test and a fix are their own to order.
| Homes | Custer County | Colorado |
|---|---|---|
| Housing units | 4,349 | 2,545,124 |
| Detached houses | 88% | 62% |
| In buildings of 5 or more | 2% | 22% |
| Mobile homes | 9% | 4% |
| Built before 1960 | 17% | 16% |
| Built since 2000 | 34% | 31% |
| Middle year built | 1990 | 1987 |
| Owner-occupied | 86% | 66% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.