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 Ravalli County, Montana
EPA puts Ravalli County in Zone 1, its highest radon zone, and high results are common there: 44.6% of the 1,090 radon tests reported to CDC (2008 to 2017, laboratory totals) 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
44.6%
0.9 pts below MT
- Ravalli
- 44.6%
- Montana
- 45.5%
1,090 tests, 2008 to 2017
Median result
3.5pCi/L
Below action level
- Ravalli
- 3.5 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2008 to 2017
Tests reported
1,090
4th of 23 by tests
- Ravalli
- 1,090
- Missoula
- 2,613
Reported to CDC before any fix, 2008 to 2017
EPA radon zone
Zone 1
Highest potential
- Zone 1
- 2
- 3
1 highest, 3 lowest
EPA predicts over 4 pCi/L indoors
Rank in Montana
18 of 23
Lowest quarter
- Ravalli
- 44.6%
- Richland
- 78.6%
By share, of 23 with 30+ tests
Read a result for Ravalli County
Starts at Ravalli 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. Ravalli County's median reported result, 2008 to 2017.
The data
Ravalli County, At a glance
Ravalli County at a glance
Predicted: EPA radon zone
EPA Zone 1: highest predicted potential
EPA puts all of Ravalli 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 Ravalli County, 2008 to 2017, laboratory
Under 2 pCi/L: 31%2 to 4 pCi/L: 24%4 pCi/L and above: 45%
Of 1,090 pre-mitigation tests reported to CDC, not homes in this area.
| Result band | Tests Measured | Share Measured |
|---|---|---|
| Under 2 pCi/L | 340 | 31.2% |
| 2 to 4 pCi/L | 264 | 24.2% |
| 4 pCi/L and above | 486 | 44.6% |
What these figures count
These are the 1,090 tests reported to CDC for Ravalli County over 2008 to 2017 (laboratory totals), 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: 2008 to 2017, laboratory. Measured data period: 2005 to 2017 (every CDC figure on file).
Ravalli County, Compared
Ravalli County radon figures, compared
Calculated by Radon411In Ravalli County, about 4 in 10 reported tests over the 2008 to 2017 laboratory totals (486 of 1,090) were at or above EPA's action level. Against the national pool of 35.7%, the gap is 8.9 points higher. Across 51 Montana counties pooled together, 45.5% of tests reached that level, so Ravalli County runs 0.9 points below its state.
Of 4 neighbours with a figure, 2 reported a larger share at or above 4 pCi/L and 1 a smaller one; the spread is 40.0% (Idaho County, ID) to 65.2% (Lemhi County, ID). By share, Ravalli County is 18th of 23 Montana counties with 30 or more tests for the same period.
Half the tests came in under 3.5 pCi/L and half over it; the single highest reached 145.0 pCi/L. Below the action level, 340 tests (31.2%) came in under 2 pCi/L, against 29.2% statewide, and 264 tests (24.2%) fell between 2 and 4, against 25.2% statewide.
Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 44.6% share point the same way here. USGS geology rates 100% of the county's land high radon potential. CDC also counts 14 tests taken after mitigation in Ravalli County for the same period: tests in homes where a fix was already in.
CDC's ten-year totals for Ravalli County went from 936 tests (2005 to 2014) to 1,090 (2008 to 2017), the share going from 43.9% to 44.6%.
Pooled shares: Radon411's sum of CDC's county counts for one period.
Ravalli County, Geology
The ground under Ravalli County
PredictedUSGS's geologic map puts all of Ravalli County's mapped land in one class: high radon potential. All of it lies in the area the map calls Northern Rocky Mountains, to which USGS gives a radon index of 13, in the high band (12 to 17).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Northern Rocky Mountains | Granitic, metaigneous, metasedimentary rocks, valley fill colluvium and alluvium. | High | 13 | 99.8% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Ravalli County beside the ground around it
Ravalli County has more high-potential ground than Montana as a whole: 100% of its land against 78.5%. Of the 6 counties that border it, none has as large a share of high-potential ground; Deer Lodge County comes nearest at 100%.
The map rates the ground, not the air in any home.
Local help
Ravalli County, Local resources
Radon testing and mitigation in Ravalli County
- Radon Control ProgramRadon Control Program, run by Montana DEQ, does not license radon professionals and offers free or discounted test kits, and answers questions about testing and mitigation in Montana.Visit the program’s page(opens in a new tab)
- Free and low-cost kitsThe program says:
Energy Bureau staff manage the radon information toll-free hotline and distribute subsidized radon test kits to Montana residents.
- Compare kits
- See the Montana directoryNo professionals are listed in Montana yet. The state program can point you to registered testers and mitigators.
What Montana's program says
- Phone
- 1-800-546-0483
- Licensing of radon professionals
Montana DEQ does not certify or require proof of certification for the contractors listed.
What it means
Ravalli County, Questions
Questions about radon in Ravalli County
Are radon levels high in Ravalli County?
Over the 2008 to 2017 laboratory totals, 44.6% of the radon tests reported to CDC for Ravalli County, Montana were at or above 4 pCi/L, and the median reported pre-mitigation result was 3.5 pCi/L. Of 23 Montana counties with 30 or more tests for the same period, 17 reported a higher share; pooled, the state comes to 45.5%.
Which counties border Ravalli County?
Ravalli County borders 6 counties: Granite County, MT, Deer Lodge County, MT, Missoula County, MT, Idaho County, ID, Lemhi County, ID and Beaverhead County, MT.
Products
Ravalli County, Products
Testing a home in Ravalli County
In Ravalli County, 44.6% of 1,090 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 45.5% pooled across Montana. In Zone 1 the year-round level in Ravalli 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
RM-63Pro rechargeable radon monitor with a touchscreen
- C-NRPP 2024/25: Not included
- Battery
- Alarm
- Screen
Method: Semiconductor sensor
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
Ravalli County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Ravalli County
Explore
Ravalli County, Bordering counties
Counties bordering Ravalli County
Calculated by Radon411- Radon levels in Lemhi County, IDEPA zone 1
65.2%at or above 4 pCi/L
Median 5.2 pCi/L · 112 tests · 20.6 points above Ravalli County
- Radon levels in Beaverhead County, MTEPA zone 1
59.5%at or above 4 pCi/L
Median 5.0 pCi/L · 37 tests · 14.9 points above Ravalli County
- Radon levels in Missoula County, MTEPA zone 1
44.6%at or above 4 pCi/L
Median 3.4 pCi/L · 2,613 tests · 0.0 points above Ravalli County
- Radon levels in Idaho County, IDEPA zone 1
40.0%at or above 4 pCi/L
Median 2.9 pCi/L · 90 tests · 4.6 points below Ravalli County
- Radon levels in Deer Lodge County, MTEPA zone 1
30.8%at or above 4 pCi/L
Median 3.4 pCi/L · 13 tests · 13.8 points below Ravalli County
- Radon levels in Granite County, MTEPA zone 1
25.0%at or above 4 pCi/L
Median 2.1 pCi/L · 8 tests · 19.6 points below Ravalli County
Ravalli County, Cities and towns
Cities and towns in Ravalli County
Ravalli County is growing: the Census Bureau puts it at 48,582 residents on July 1, 2025, up 9.4% from 44,412 in 2020. That works out to 20 people per square mile of land. No town dominates: Hamilton, the largest, has 5,451 residents, 11.2% of the total. Together its 4 incorporated places hold 19.5% of those residents; the other 80.5% live outside any of them. Testing is reported here more often than across the state: CDC's 1,090 reported tests for 2008 to 2017 come to 22.4 for every 1,000 residents (2025 estimate), against 8.6 for Montana.
From Hamilton to Pinesdale, CDC publishes no figure by town: each reads Ravalli County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Hamilton | 5,451 | +15.5% | 11.2% |
| Stevensville | 2,259 | +11.8% | 4.6% |
| Darby | 888 | +11.7% | 1.8% |
| Pinesdale | 882 | +8.5% | 1.8% |
4 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).
Ravalli County, Homes
Homes in Ravalli County
Ravalli County is a place of houses on their own lots: 80% of its 21,098 homes are detached single-family houses, against 69% across Montana. Much of Ravalli County is recent building: 28% of its homes have gone up since 2000 and the middle year built is 1990, against 1980 for Montana. Owners live in 79% of the occupied homes (Montana: 69%), so for most households a test and a fix are their own to order.
| Homes | Ravalli County | Montana |
|---|---|---|
| Housing units | 21,098 | 522,939 |
| Detached houses | 80% | 69% |
| In buildings of 5 or more | 4% | 9% |
| Mobile homes | 8% | 10% |
| Built before 1960 | 16% | 26% |
| Built since 2000 | 28% | 27% |
| Middle year built | 1990 | 1980 |
| Owner-occupied | 79% | 69% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.