Short-term kit
Air Chek Short-Term radon test kit you hang, lab fee included
- Lab fee included
In home: 72 to 168 hours
Locations and reports
Radon Levels in Madison County, Idaho
EPA puts Madison County in Zone 2, its middle radon zone, and high results are common there: 63.7% of the 314 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
63.7%
22.2 pts above ID
- Madison
- 63.7%
- Idaho
- 41.5%
314 tests, 2008 to 2017
Median result
6.2pCi/L
Action level reached
- Madison
- 6.2 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2008 to 2017
Tests reported
314
11th of 37 by tests
- Madison
- 314
- Ada
- 3,030
Reported to CDC before any fix, 2008 to 2017
EPA radon zone
Zone 2
Moderate potential
- 1
- Zone 2
- 3
1 highest, 3 lowest
EPA predicts 2 to 4 pCi/L indoors
Rank in Idaho
5 of 37
Top quarter
- Madison
- 63.7%
- Bear Lake
- 78.1%
By share, of 37 with 30+ tests
Read a result for Madison County
Starts at Madison County's median, 6.2 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 6.2 pCi/L
At or above 4 pCi/L
- Under 20 to 1.9 pCi/L
- 2 to 4consider a fix
- 4 and aboveEPA says fix it
This result is at or above 4 pCi/L. EPA recommends fixing a home when the radon level is 4 pCi/L or higher. 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 2: moderate predicted potential
Madison County is a
USGS geologic potential: High across 58% 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: 20%2 to 4 pCi/L: 16%4 pCi/L and above: 64%
Of 314 pre-mitigation tests reported to CDC, not homes in this area.
| Result band | Tests Measured | Share Measured |
|---|---|---|
| Under 2 pCi/L | 62 | 19.7% |
| 2 to 4 pCi/L | 52 | 16.6% |
| 4 pCi/L and above | 200 | 63.7% |
What these figures count
These are the 314 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: 63.7% of the 314 radon tests reported to CDC for Madison County over the 2008 to 2017 laboratory totals read at least 4 pCi/L. That places it 5th of 37 Idaho counties with 30 or more tests for the same period. That is 22.2 points above the 41.5% pooled from 44 Idaho counties.
The median result, 6.2 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 52.5 pCi/L. The rest split 19.7% under 2 pCi/L and 16.6% from 2 to 4 (Idaho: 31.5% and 26.9%). The reported tests do not follow EPA's Zone 2 label for Madison County (predicted average between 2 and 4 pCi/L): 63.7% of them reached 4 pCi/L, fewer than that label suggests.
1 of its 4 bordering counties with figures ran higher, led by Jefferson County at 67.1%; Bonneville County reported 40.1%. Statewide for the same period, Bear Lake County reported the highest share (78.1%) and Payette County the lowest (4.9%).
CDC's ten-year totals for Madison County went from 215 tests (2005 to 2014) to 314 (2008 to 2017), the share going from 67.9% to 63.7%.
Nationally, every county with a figure for the same period pools to 35.7%; Madison County sits 28.0 points above it. CDC also counts 19 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 splits Madison County: 58.1% of its land is high radon potential and 41.9% moderate. The map puts 58.1% of Madison County in the area it calls Middle Rocky Mts./Yellowstone and 37.6% in Eastern Snake river plain and Malheur-Boise-King Section, with one smaller area beside them. USGS gives the first a radon index of 12, in the high band (12 to 17), and the second 10, in the moderate band (9 to 11).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Middle Rocky Mts./Yellowstone | Extrusive volcanics, rhyolite flows, variable composition. | High | 12 | 58.1% |
| Eastern Snake river plain and Malheur-Boise-King Section | Basalt flows. | Moderate | 10 | 37.6% |
| Middle Rocky Mountain province | Complexly folded, faulted, and metamorphosed rocks of volcanic origin. | Moderate | 11 | 4.3% |
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
On high-potential ground Madison County is close to Idaho as a whole: 58.1% of its land against 50.7%. Of the 4 counties that border it, 1 has more high-potential ground, Fremont County the most at 68.2%.
The map rates the ground, not the air in any home.
Local help
Madison County, Local resources
Radon testing and mitigation in Madison County
- DHW Environmental Health ProgramDHW Environmental Health Program, run by Idaho Department of Health and Welfare, offers free or discounted test kits, and answers questions about testing and mitigation in Idaho.Visit the program’s page(opens in a new tab)
- Free and low-cost kitsThe program says:
Order a free radon test kit.
- Compare kits
- See the Idaho directoryNo professionals are listed in Idaho yet. The state program can point you to registered testers and mitigators.
What Idaho's program says
- Phone
- 800-445-8647
- radon@dhw.idaho.gov
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, 63.7% of the radon tests reported to CDC for Madison County, Idaho were at or above 4 pCi/L, and the median reported pre-mitigation result was 6.2 pCi/L. Of 37 Idaho counties with 30 or more tests for the same period, 4 reported a higher share; pooled, the state comes to 41.5%.
Which counties border Madison County?
Madison County borders 4 counties: Teton County, Jefferson County, Bonneville County and Fremont County.
Products
Madison County, Products
Testing a home in Madison County
In Madison County, 63.7% of 314 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 41.5% pooled across Idaho. In Zone 2 a short-term kit (2 to 90 days) is the quick first check in Madison County; a long-term test tells the year-round average.
Test kits and monitors3
See every kit and monitor
Long-term kit
RL116 long-term radon test kit
- Lab fee extra
Method: Alpha track
In home: 90 days to 12 months
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
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Explore
Madison County, Bordering counties
Counties bordering Madison County
Calculated by Radon411- Radon levels in Jefferson CountyEPA zone 2
67.1%at or above 4 pCi/L
Median 5.7 pCi/L · 207 tests · 3.4 points above Madison County
- Radon levels in Teton CountyEPA zone 2
53.3%at or above 4 pCi/L
Median 4.4 pCi/L · 473 tests · 10.4 points below Madison County
- Radon levels in Fremont CountyEPA zone 1
49.5%at or above 4 pCi/L
Median 3.9 pCi/L · 101 tests · 14.2 points below Madison County
- Radon levels in Bonneville CountyEPA zone 2
40.1%at or above 4 pCi/L
Median 3.4 pCi/L · 1,117 tests · 23.6 points below Madison County
Madison County, Cities and towns
Cities and towns in Madison County
The Census Bureau estimates 55,172 residents in Madison County for July 1, 2025, 2,222 more than in 2020 (+4.2%). That works out to 118 people per square mile of land. Rexburg alone is home to 40,334 of them, 73.1% of the total. Together its 2 incorporated places hold 77.6% of those residents; the other 22.4% live outside any of them. CDC's 314 reported tests for 2008 to 2017 work out to 5.7 per 1,000 residents (2025 estimate), close to Idaho's 6.4.
From Rexburg to Sugar City, CDC publishes no figure by town: each reads Madison County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Rexburg | 40,334 | +1.3% | 73.1% |
| Sugar City | 2,476 | +42.6% | 4.5% |
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).
Madison County, Homes
Homes in Madison County
Madison County has 14,769 homes, and many share a building: 41% are in buildings of five or more, 38% are detached houses, against 74% across Idaho. Much of Madison County is recent building: 55% of its homes have gone up since 2000 and the middle year built is 2002, against 1990 for Idaho. Most occupied homes here are rented: owners live in 40% (Idaho: 72%). A tenant can run a test; a fix is the landlord's to make.
| Homes | Madison County | Idaho |
|---|---|---|
| Housing units | 14,769 | 776,683 |
| Detached houses | 38% | 74% |
| In buildings of 5 or more | 41% | 9% |
| Mobile homes | 5% | 7% |
| Built before 1960 | 8% | 18% |
| Built since 2000 | 55% | 35% |
| Middle year built | 2002 | 1990 |
| Owner-occupied | 40% | 72% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.