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 Madison County, Montana
EPA puts Madison County in Zone 1, its highest radon zone, and high results are common there: 50.0% of the 58 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
50.0%
4.5 pts above MT
- Madison
- 50.0%
- Montana
- 45.5%
58 tests, 2008 to 2017
Median result
3.9pCi/L
Below action level
- Madison
- 3.9 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2008 to 2017
Tests reported
58
17th of 23 by tests
- Madison
- 58
- 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
14 of 23
Middle half
- Madison
- 50.0%
- Richland
- 78.6%
By share, of 23 with 30+ tests
Read a result for Madison County
Starts at Madison County's median, 3.9 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 3.9 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. Madison County's median reported result, 2008 to 2017.
The data
Madison County, At a glance
Madison County at a glance
Predicted: EPA radon zone
EPA Zone 1: highest predicted potential
EPA puts all of Madison 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 Madison County, 2008 to 2017, laboratory
Under 2 pCi/L: 31%2 to 4 pCi/L: 19%4 pCi/L and above: 50%
Of 58 pre-mitigation tests reported to CDC, not homes in this area.
| Result band | Tests Measured | Share Measured |
|---|---|---|
| Under 2 pCi/L | 18 | 31.0% |
| 2 to 4 pCi/L | 11 | 19.0% |
| 4 pCi/L and above | 29 | 50.0% |
What these figures count
These are the 58 tests reported to CDC for Madison 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).
Madison County, Compared
Madison County radon figures, compared
Calculated by Radon411More than half: 50.0% of the 58 radon tests reported to CDC for Madison County over the 2008 to 2017 laboratory totals read at least 4 pCi/L. That places it 14th of 23 Montana counties with 30 or more tests for the same period. That is 4.5 points above the 45.5% pooled from 51 Montana counties.
The median result, 3.9 pCi/L, sits between 2 and EPA's 4 pCi/L action level, and the top reported result was 24.4 pCi/L. The rest split 31.0% under 2 pCi/L and 19.0% from 2 to 4 (Montana: 29.2% and 25.2%). Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 50.0% share point the same way here.
3 of its 5 bordering counties with figures ran higher, led by Jefferson County at 71.0%; Gallatin County reported 42.8%. Statewide for the same period, Richland County reported the highest share (78.6%) and Cascade County the lowest (29.4%).
CDC's ten-year totals for Madison County went from 38 tests (2005 to 2014) to 58 (2008 to 2017), the share going from 50.0% to 50.0%.
Nationally, every county with a figure for the same period pools to 35.7%; Madison County sits 14.3 points above it. CDC also counts 5 tests taken after mitigation in Madison County for the same period: tests in homes where a fix was already in.
Pooled shares: Radon411's sum of CDC's county counts for one period.
Madison County, Geology
The ground under Madison County
PredictedUSGS's geologic map puts all of Madison 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 | 100% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Madison County beside the ground around it
Madison County has more high-potential ground than Montana as a whole: 100% of its land against 78.5%. Of the 5 counties that border it, none has as large a share of high-potential ground; Jefferson County comes nearest at 100%.
The map rates the ground, not the air in any home.
Local help
Madison County, Local resources
Radon testing and mitigation in Madison 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
Madison County, Questions
Questions about radon in Madison County
Are radon levels high in Madison County?
Over the 2008 to 2017 laboratory totals, 50.0% of the radon tests reported to CDC for Madison County, Montana were at or above 4 pCi/L, and the median reported pre-mitigation result was 3.9 pCi/L. Of 23 Montana counties with 30 or more tests for the same period, 13 reported a higher share; pooled, the state comes to 45.5%.
Which counties border Madison County?
Madison County borders 5 counties: Gallatin County, MT, Beaverhead County, MT, Silver Bow County, MT, Jefferson County, MT and Fremont County, ID.
Products
Madison County, Products
Testing a home in Madison County
In Madison County, 50.0% of 58 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 Madison 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
EcoQube Flex 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 15 minutes
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
Madison County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Madison County
Explore
Madison County, Bordering counties
Counties bordering Madison County
Calculated by Radon411- Radon levels in Jefferson County, MTEPA zone 1
71.0%at or above 4 pCi/L
Median 6.3 pCi/L · 62 tests · 21.0 points above Madison County
- Radon levels in Silver Bow County, MTEPA zone 1
70.1%at or above 4 pCi/L
Median 6.0 pCi/L · 174 tests · 20.1 points above Madison County
- Radon levels in Beaverhead County, MTEPA zone 1
59.5%at or above 4 pCi/L
Median 5.0 pCi/L · 37 tests · 9.5 points above Madison County
- Radon levels in Fremont County, IDEPA zone 1
49.5%at or above 4 pCi/L
Median 3.9 pCi/L · 101 tests · 0.5 points below Madison County
- Radon levels in Gallatin County, MTEPA zone 1
42.8%at or above 4 pCi/L
Median 3.2 pCi/L · 1,600 tests · 7.2 points below Madison County
Madison County, Cities and towns
Cities and towns in Madison County
Madison County is growing: the Census Bureau puts it at 10,026 residents on July 1, 2025, up 15.8% from 8,657 in 2020. Spread over its land, that is 2.8 people to the square mile. No town dominates: Ennis, the largest, has 1,126 residents, 11.2% of the total. Together its 4 incorporated places hold 25.9% of those residents; the other 74.1% live outside any of them. CDC's 58 reported tests for 2008 to 2017 work out to 5.8 per 1,000 residents (2025 estimate), close to Montana's 8.6.
From Ennis to Virginia City, CDC publishes no figure by town: each reads Madison County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Ennis | 1,126 | +21.3% | 11.2% |
| Sheridan | 779 | +13.7% | 7.8% |
| Twin Bridges | 430 | +25.4% | 4.3% |
| Virginia City | 260 | +19.3% | 2.6% |
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).
Madison County, Homes
Homes in Madison County
Madison County is a place of houses on their own lots: 77% of its 6,405 homes are detached single-family houses, against 69% across Montana. Much of Madison County is recent building: 37% of its homes have gone up since 2000 and the middle year built is 1993, against 1980 for Montana. Owners live in 81% of the occupied homes (Montana: 69%), so for most households a test and a fix are their own to order.
| Homes | Madison County | Montana |
|---|---|---|
| Housing units | 6,405 | 522,939 |
| Detached houses | 77% | 69% |
| In buildings of 5 or more | 4% | 9% |
| Mobile homes | 7% | 10% |
| Built before 1960 | 17% | 26% |
| Built since 2000 | 37% | 27% |
| Middle year built | 1993 | 1980 |
| Owner-occupied | 81% | 69% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.