Radon levels in Madison County, Idaho
HighEPA Zone 2Predicted long-term basement average of 4.3 pCi/L (model estimate) across 4 ZIP codes - about 2.4× the US average of 1.8, about 1.6× the Idaho average of 2.6. Ranked #2 of 44 Idaho counties.
Test Madison County, ID now - and consider a continuous monitor
The model predicts a long-term basement average of 4.3 pCi/L here, at or above the EPA action level of 4. Homes in the same ZIP still vary widely, so a real test is the only way to know your number. A continuous digital monitor shows how your level swings with weather and season, which matters when you're near the action level.
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Already tested at 4 pCi/L or higher? Find a certified mitigation professional (EPA). A mitigation system typically runs $800-$2,500 installed.
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Predicted (model estimate). The pCi/L figures on this page are long-term area averages from a peer-reviewed national model built on millions of real radon tests (2001-2021). They describe the typical home in this area - not your home, which can be several times higher or lower. The EPA radon zone is a separate, 1993 county-level classification. Measured state test results are shown separately below, labeled with their source and years. How the numbers work.
4.3 ± 0.07
pCi/L predicted basement mean (model SD)
2.3 ± 0.08
pCi/L predicted upstairs (above-ground) mean
2.8-4.4
range of ZIP-level basement predictions in the county
Measured radon tests in Madison County (Idaho Department of Health and Welfare, through 2019)
Actual results from home radon tests reported to the state, separate from the model estimate above. Coverage: through 2019 (start year not stated by the source).
- Measured mean
- 8.6 pCi/L
- Results ≥ 4 pCi/L
- 34.1%
- Sample
- 1,378 tests
| Figure | Model (predicted) | State tests (measured) |
|---|---|---|
| Mean, pCi/L | 4.3 basement | 8.6 |
| Share ≥ 4 pCi/L | not a model output | 34.1% |
The measured mean runs 4.4 pCi/L above the model because state test data is voluntary and skews toward basements, winter, and homeowners who already suspected a problem, while the model estimates the long-term average across all homes.
Source: Home Radon Test Results by Zip Code, Idaho Department of Health and Welfare, Indoor Environment / Radon Program. No license statement on the public feature service (publicly shared by the IDHW environmental-health account). Method and download.
Tested above 4 pCi/L? Get a mitigation quote from a certified local contractor
Typical mitigation runs $800-$2,500 and takes a day. Installers guarantee the system brings levels under 4 pCi/L. Tell us where you are in Madison County, ID and a certified mitigator will follow up - no obligation.
What this means for Madison
The typical home in Madison County is predicted to sit at or above the EPA action level of 4 pCi/L in the basement. In practice that means a large share of houses here would qualify for mitigation if tested, and buyers routinely ask for radon tests in Idaho transactions.
Note that the EPA classifies Madison County as Zone 2 while the newer model predicts 4.3 pCi/L. The zone map predates two decades of test data; where they disagree, we grade on the model but show both. County figures weight each ZIP by its 2010 Census population, so they describe where people live rather than empty land.
Comparable Idaho counties: Teton County (4.4), Jefferson County (4.0), Custer County (3.7), Kootenai County (3.7). The state's highest is Teton County at 4.4 pCi/L.
ZIP codes in Madison County
Predicted basement and upstairs means by ZIP (model estimate). ZIPs whose land is mostly in this county.
If your test comes back at 4 pCi/L or higher
Mitigation is a routine job: a fan-driven pipe that vents soil gas from under the slab to above the roofline, typically $800-$2,500 installed (typical range; local quotes vary). Use certified professionals: EPA find-a-professional. Read the full mitigation guide.
Madison County radon questions
- Is radon high in Madison County, Idaho?
- High. The model predicts a long-term basement average of 4.3 pCi/L in Madison County (about 2.4× the US average of 1.8 and about 1.6× the Idaho average of 2.6). That is at or above the EPA action level of 4 pCi/L, so the typical home here would qualify for mitigation. Ranked 2 of 44 Idaho counties.
- What do actual radon tests show in Madison County?
- Idaho Department of Health and Welfare data covering through 2019 (1,378 tests) shows an average of 8.6 pCi/L, 34.1% of results at or above the 4 pCi/L action level. These are voluntary home tests, so they skew toward basements and toward homes where radon was suspected; the model's predicted long-term basement average for the county is 4.3 pCi/L.
- Should I test for radon in Madison County?
- Yes, soon. With a predicted average of 4.3 pCi/L and at least one ZIP predicted at 4.4, many homes in Madison County will test above the 4 pCi/L action level. Use a short-term kit first; if it reads 2 or higher, confirm with a long-term test or continuous monitor before deciding on mitigation.
- What does EPA Radon Zone 2 mean for Madison County?
- Zone 2 - moderate potential (2-4 pCi/L). The zone map dates from 1993 and classifies whole counties. The newer model's predicted average of 4.3 pCi/L does not line up with Zone 2, which is common - the EPA itself says high-radon homes exist in every zone. Neither replaces a test of your own home.
- How much does radon mitigation cost in Madison County?
- A standard active sub-slab depressurization system typically runs $800-$2,500 installed nationally; Idaho quotes vary with foundation type (slab, crawlspace, basement), home size and local labor. Get two or three bids from certified mitigators listed by your state radon program or the EPA's find-a-professional page.
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