Montana Radon Levels
50Zone 1 (High)
7Zone 2 (Moderate)
0Zone 3 (Low)
88% of counties in Montana are classified as EPA Zone 1 (highest radon potential), meaning predicted average indoor radon levels exceed 4 pCi/L — the EPA action level. The EPA recommends that all homes be tested for radon, regardless of zone classification.
| County | EPA Zone | Risk Level |
|---|---|---|
| Beaverhead County | Zone 1 | Highest Potential |
| Big Horn County | Zone 1 | Highest Potential |
| Blaine County | Zone 1 | Highest Potential |
| Broadwater County | Zone 1 | Highest Potential |
| Carbon County | Zone 1 | Highest Potential |
| Carter County | Zone 1 | Highest Potential |
| Cascade County | Zone 1 | Highest Potential |
| Chouteau County | Zone 1 | Highest Potential |
| Custer County | Zone 1 | Highest Potential |
| Daniels County | Zone 1 | Highest Potential |
| Dawson County | Zone 1 | Highest Potential |
| Deer Lodge County | Zone 1 | Highest Potential |
| Fallon County | Zone 1 | Highest Potential |
| Fergus County | Zone 1 | Highest Potential |
| Flathead County | Zone 1 | Highest Potential |
| Gallatin County | Zone 1 | Highest Potential |
| Garfield County | Zone 1 | Highest Potential |
| Glacier County | Zone 1 | Highest Potential |
| Golden Valley County | Zone 2 | Moderate Potential |
| Granite County | Zone 1 | Highest Potential |
| Hill County | Zone 1 | Highest Potential |
| Jefferson County | Zone 1 | Highest Potential |
| Judith Basin County | Zone 1 | Highest Potential |
| Lake County | Zone 1 | Highest Potential |
| Lewis and Clark County | Zone 1 | Highest Potential |
| Liberty County | Zone 1 | Highest Potential |
| Lincoln County | Zone 1 | Highest Potential |
| McCone County | Zone 1 | Highest Potential |
| Madison County | Zone 1 | Highest Potential |
| Meagher County | Zone 1 | Highest Potential |
| Mineral County | Zone 1 | Highest Potential |
| Missoula County | Zone 1 | Highest Potential |
| Musselshell County | Zone 2 | Moderate Potential |
| Park County | Zone 1 | Highest Potential |
| Petroleum County | Zone 2 | Moderate Potential |
| Phillips County | Zone 1 | Highest Potential |
| Pondera County | Zone 1 | Highest Potential |
| Powder River County | Zone 1 | Highest Potential |
| Powell County | Zone 1 | Highest Potential |
| Prairie County | Zone 1 | Highest Potential |
| Ravalli County | Zone 1 | Highest Potential |
| Richland County | Zone 1 | Highest Potential |
| Roosevelt County | Zone 1 | Highest Potential |
| Rosebud County | Zone 1 | Highest Potential |
| Sanders County | Zone 1 | Highest Potential |
| Sheridan County | Zone 1 | Highest Potential |
| Silver Bow County | Zone 1 | Highest Potential |
| Stillwater County | Zone 1 | Highest Potential |
| Sweet Grass County | Zone 2 | Moderate Potential |
| Teton County | Zone 1 | Highest Potential |
| Toole County | Zone 1 | Highest Potential |
| Treasure County | Zone 2 | Moderate Potential |
| Valley County | Zone 1 | Highest Potential |
| Wheatland County | Zone 2 | Moderate Potential |
| Wibaux County | Zone 1 | Highest Potential |
| Yellowstone County | Zone 2 | Moderate Potential |
| Yellowstone National Park, MT | Zone 1 | Highest Potential |