Radon levels in Montana: Moderate
The model predicts a population-weighted basement average of 3.1 pCi/L across Montana's 56 counties - about 1.7× the US average of 1.8 pCi/L. Above-ground floors average 2.1 pCi/L.
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. How the numbers work.
49 / 56
EPA Zone 1 counties (88%)
7 / 0
Zone 2 / Zone 3 counties
1
counties predicted ≥ 4 pCi/L
1%
of ZIP codes predicted ≥ 4 pCi/L
Montana counties by predicted radon
Sorted highest to lowest predicted basement average. 56 counties.
| County | Predicted basement | Upstairs | Grade | EPA zone | ZIPs |
|---|---|---|---|---|---|
| Park County | 4.2 pCi/L | 2.5 | High | EPA Zone 1 | 6 |
| Silver Bow County | 4.0 pCi/L | 2.5 | Moderate | EPA Zone 1 | 3 |
| Fergus County | 3.6 pCi/L | 2.5 | Moderate | EPA Zone 1 | 9 |
| Judith Basin County | 3.5 pCi/L | 2.1 | Moderate | EPA Zone 1 | 6 |
| Lewis and Clark County | 3.5 pCi/L | 2.7 | Moderate | EPA Zone 1 | 7 |
| Daniels County | 3.5 pCi/L | 2.4 | Moderate | EPA Zone 1 | 4 |
| Powell County | 3.5 pCi/L | 2.5 | Moderate | EPA Zone 1 | 5 |
| Wibaux County | 3.5 pCi/L | 2.1 | Moderate | EPA Zone 1 | 1 |
| Deer Lodge County | 3.4 pCi/L | 2.6 | Moderate | EPA Zone 1 | 3 |
| Lincoln County | 3.4 pCi/L | 2.2 | Moderate | EPA Zone 1 | 4 |
| Valley County | 3.4 pCi/L | 2.2 | Moderate | EPA Zone 1 | 7 |
| Custer County | 3.3 pCi/L | 2.2 | Moderate | EPA Zone 1 | 3 |
| Flathead County | 3.3 pCi/L | 2.3 | Moderate | EPA Zone 1 | 10 |
| Chouteau County | 3.3 pCi/L | 2.2 | Moderate | EPA Zone 1 | 7 |
| Toole County | 3.3 pCi/L | 2.1 | Moderate | EPA Zone 1 | 6 |
| Pondera County | 3.3 pCi/L | 2.3 | Moderate | EPA Zone 1 | 4 |
| Ravalli County | 3.3 pCi/L | 2.5 | Moderate | EPA Zone 1 | 8 |
| Blaine County | 3.3 pCi/L | 2.1 | Moderate | EPA Zone 1 | 6 |
| Granite County | 3.3 pCi/L | 2.5 | Moderate | EPA Zone 1 | 4 |
| Phillips County | 3.3 pCi/L | 2.2 | Moderate | EPA Zone 1 | 6 |
| Prairie County | 3.3 pCi/L | 2.1 | Moderate | EPA Zone 1 | 2 |
| Broadwater County | 3.2 pCi/L | 2.3 | Moderate | EPA Zone 1 | 3 |
| Sheridan County | 3.2 pCi/L | 2.0 | Moderate | EPA Zone 1 | 10 |
| McCone County | 3.2 pCi/L | 2.0 | Moderate | EPA Zone 1 | 4 |
| Teton County | 3.2 pCi/L | 2.3 | Moderate | EPA Zone 1 | 6 |
| Meagher County | 3.2 pCi/L | 2.3 | Moderate | EPA Zone 1 | 3 |
| Jefferson County | 3.2 pCi/L | 2.5 | Moderate | EPA Zone 1 | 4 |
| Liberty County | 3.2 pCi/L | 2.1 | Moderate | EPA Zone 1 | 4 |
| Richland County | 3.1 pCi/L | 2.1 | Moderate | EPA Zone 1 | 4 |
| Carbon County | 3.1 pCi/L | 2.0 | Moderate | EPA Zone 1 | 8 |
| Garfield County | 3.1 pCi/L | 1.9 | Moderate | EPA Zone 1 | 6 |
| Madison County | 3.1 pCi/L | 2.3 | Moderate | EPA Zone 1 | 9 |
| Roosevelt County | 3.1 pCi/L | 1.9 | Moderate | EPA Zone 1 | 6 |
| Beaverhead County | 3.1 pCi/L | 2.3 | Moderate | EPA Zone 1 | 5 |
| Musselshell County | 3.1 pCi/L | 1.7 | Moderate | EPA Zone 2 | 2 |
| Carter County | 3.0 pCi/L | 2.0 | Moderate | EPA Zone 1 | 3 |
| Sweet Grass County | 3.0 pCi/L | 1.8 | Moderate | EPA Zone 2 | 4 |
| Golden Valley County | 3.0 pCi/L | 1.8 | Moderate | EPA Zone 2 | 2 |
| Missoula County | 3.0 pCi/L | 2.3 | Moderate | EPA Zone 1 | 12 |
| Wheatland County | 3.0 pCi/L | 1.8 | Moderate | EPA Zone 2 | 3 |
| Powder River County | 3.0 pCi/L | 1.9 | Moderate | EPA Zone 1 | 6 |
| Mineral County | 3.0 pCi/L | 2.2 | Moderate | EPA Zone 1 | 4 |
| Fallon County | 3.0 pCi/L | 2.0 | Moderate | EPA Zone 1 | 3 |
| Petroleum County | 3.0 pCi/L | 1.8 | Moderate | EPA Zone 2 | 1 |
| Sanders County | 3.0 pCi/L | 2.1 | Moderate | EPA Zone 1 | 8 |
| Stillwater County | 3.0 pCi/L | 1.9 | Moderate | EPA Zone 1 | 8 |
| Yellowstone County | 3.0 pCi/L | 1.9 | Moderate | EPA Zone 2 | 12 |
| Glacier County | 2.9 pCi/L | 2.0 | Moderate | EPA Zone 1 | 4 |
| Lake County | 2.9 pCi/L | 2.0 | Moderate | EPA Zone 1 | 10 |
| Rosebud County | 2.8 pCi/L | 1.7 | Moderate | EPA Zone 1 | 6 |
| Big Horn County | 2.8 pCi/L | 1.8 | Moderate | EPA Zone 1 | 9 |
| Hill County | 2.7 pCi/L | 2.0 | Moderate | EPA Zone 1 | 7 |
| Treasure County | 2.7 pCi/L | 1.8 | Moderate | EPA Zone 2 | 3 |
| Dawson County | 2.6 pCi/L | 1.8 | Moderate | EPA Zone 1 | 4 |
| Cascade County | 2.5 pCi/L | 1.9 | Moderate | EPA Zone 1 | 13 |
| Gallatin County | 2.3 pCi/L | 2.0 | Moderate | EPA Zone 1 | 7 |
Montana radon questions
- Is radon high in Montana?
- Montana's population-weighted predicted basement average is 3.1 pCi/L, about 1.7× the US average of 1.8. 1 of its 56 modeled counties are predicted at or above the EPA action level of 4 pCi/L, 55 are in the 2-4 "consider fixing" range and 0 are below 2. 1% of Montana ZIP codes are predicted at 4 or higher.
- Which Montana county has the highest radon?
- Park County has the highest predicted basement average in Montana at 4.2 pCi/L (EPA Zone 1). The lowest is Gallatin County at 2.3 pCi/L. These are modeled area averages; individual homes in any county can test far higher.
- How many EPA Zone 1 counties are in Montana?
- 49 of Montana's 56 counties (88%) are EPA Zone 1 (highest potential), 7 are Zone 2 and 0 are Zone 3. The EPA zone map dates from 1993; the predicted values on this page come from a 2001-2021 model built on millions of actual tests, so the two can disagree for a given county.
- Should I test for radon in Montana?
- Yes - with some urgency. Montana's predicted average is in the moderate range, and 99.4% of its ZIP codes are predicted at 2 pCi/L or higher. A short-term charcoal kit or a continuous digital monitor will tell you your actual level within days.
Montana radon program
Many states offer free or discounted test kits and keep lists of certified mitigators. Find the Montana radon office through the EPA state radon contacts page. Then read how to test and what mitigation costs.