Radon levels in Montana: Moderate
The model predicts a population-weighted basement average of 3.1 pCi/L (model estimate) 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
Test Montana - the EPA says "consider fixing" in this range
The predicted basement average here is 3.1 pCi/L, in the 2-4 pCi/L band where the EPA recommends considering mitigation. Plenty of individual homes in a moderate area test above 4. Start with a short-term test; if it comes back at 2 or higher, follow up with a long-term test or a continuous monitor.
Monitor link goes to the Airthings store - use code RADONGRADE-10OFF at checkout for 10% off any Airthings monitor.
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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What the data says about radon in Montana
On the EPA's 1993 radon zone map, 49 of Montana's 56 counties are EPA Zone 1 (88%), 7 are Zone 2 and 0 are Zone 3. Zone 1 - the highest-potential class, predicted screening average above 4 pCi/L - is the most common designation in Montana. That classification has not been revised since 1993; it describes counties, not homes, and elevated readings turn up in Zone 3 counties every year.
Montana models out at 3.1 pCi/L predicted basement average (moderate; 1.7× the US population-weighted average of 1.8). Of the 56 counties with predictions, 1 are predicted at or above 4 pCi/L, 55 in the 2-4 band and 0 below 2. The highest predicted county is Park County at 4.2 pCi/L; the lowest is Gallatin County at 2.3 - a 1.9 pCi/L spread that means a statewide average tells you little about any one county.
At ZIP-code resolution, 1% of Montana ZIPs are predicted at 4 pCi/L or higher in the basement and 99.4% at 2 or higher - below the national 4.2% at the action level but above the national 48.7% at 2 pCi/L. With more than half of ZIPs above 2, a test is worth doing before any purchase or renovation here.
Montana counties by predicted radon
Sorted highest to lowest predicted basement average (model estimate). 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 |
Radon levels in Montana cities
The 4 most-populous Montana places among the 1,000 largest US cities (Census incorporated places and CDPs), by population. City figures are ZIP-land-weighted means of the model's ZIP predictions (model estimate).
| City | Population | Predicted basement | Upstairs | Grade | ZIPs ≥ 4 |
|---|---|---|---|---|---|
| Billings | 120,864 | 2.9 pCi/L | 1.8 | Moderate | 0% |
| Missoula | 77,757 | 2.9 pCi/L | 2.3 | Moderate | 20% |
| Great Falls | 60,422 | 2.5 pCi/L | 1.9 | Moderate | 0% |
| Bozeman | 57,305 | 2.3 pCi/L | 2.0 | Moderate | 0% |
Highest-radon ZIP codes in Montana
The 10 Montana ZIP codes with the highest predicted basement average (model estimate), out of 314 modeled. A ZIP average is still an area figure - neighboring homes routinely test several pCi/L apart.
| ZIP | County | Predicted basement | Upstairs | Grade |
|---|---|---|---|---|
| 59047 | Park County | 4.5 pCi/L | 2.6 | High |
| 59804 | Missoula County | 4.3 pCi/L | 3.4 | High |
| 59452 | Judith Basin County | 4.2 pCi/L | 1.9 | High |
| 59701 | Silver Bow County | 4.0 pCi/L | 2.4 | Moderate |
| 59833 | Ravalli County | 3.8 pCi/L | 3.1 | Moderate |
| 59912 | Flathead County | 3.8 pCi/L | 2.3 | Moderate |
| 59602 | Lewis and Clark County | 3.8 pCi/L | 3.2 | Moderate |
| 59457 | Fergus County | 3.8 pCi/L | 2.6 | Moderate |
| 59635 | Lewis and Clark County | 3.8 pCi/L | 2.6 | Moderate |
| 59052 | Sweet Grass County | 3.7 pCi/L | 2.5 | Moderate |
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 area figures; 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
Montana's radon program page is at deq.mt.gov and, when we checked it, offered free short-term kits for child-care providers through the Choose Safe Places program. The EPA also keeps a directory of every state radon contact: EPA state radon contacts page. Then read how to test and what mitigation costs.