What's the radon risk at your address?

Free radon zone lookup for every US county, using official EPA data.

EPA Radon Zones

The EPA classifies every US county into one of three radon zones based on predicted indoor radon levels.

Zone 1

Highest Potential

> 4 pCi/L predicted

1074 counties

These counties have predicted average indoor radon levels above the EPA action level. Testing is strongly recommended.

Zone 2

Moderate Potential

2 – 4 pCi/L predicted

1034 counties

Moderate predicted levels. Many homes in these counties still test above the action level. Testing is recommended.

Zone 3

Lowest Potential

< 2 pCi/L predicted

1035 counties

Lowest predicted levels, but elevated radon has been found in homes in all three zones. The EPA recommends testing regardless.

Browse by State

Alaska 27 counties Alabama 67 counties Arkansas 75 counties Arizona 15 counties California 58 counties Colorado 64 counties Connecticut 8 counties Delaware 3 counties Florida 67 counties Georgia 159 counties Hawaii 5 counties Iowa 99 counties Idaho 44 counties Illinois 102 counties Indiana 92 counties Kansas 105 counties Kentucky 120 counties Louisiana 64 counties Massachusetts 14 counties Maryland 24 counties Maine 16 counties Michigan 83 counties Minnesota 87 counties Missouri 115 counties Mississippi 82 counties Montana 57 counties North Carolina 100 counties North Dakota 53 counties Nebraska 93 counties New Hampshire 10 counties New Jersey 21 counties New Mexico 33 counties Nevada 17 counties New York 62 counties Ohio 88 counties Oklahoma 77 counties Oregon 36 counties Pennsylvania 67 counties Rhode Island 5 counties South Carolina 46 counties South Dakota 66 counties Tennessee 95 counties Texas 254 counties Utah 29 counties Virginia 136 counties Vermont 14 counties Washington 39 counties Wisconsin 72 counties West Virginia 55 counties Wyoming 23 counties

What is Radon?

Radon is an invisible, odorless radioactive gas that comes from the natural decay of uranium in soil and rock. It seeps into homes through cracks in foundations, construction joints, and gaps around pipes.

Learn more →

Why Test?

Radon is the second leading cause of lung cancer in the United States, responsible for an estimated 21,000 deaths per year. You can't see, smell, or taste it. The only way to know your level is to test.

Testing guide →

4 pCi/L Action Level

The EPA recommends taking action to reduce radon in your home if test results are 4 picocuries per liter (pCi/L) or higher. The average outdoor level is about 0.4 pCi/L.

What the numbers mean →

Free Radon Level Lookup for Every US County

RadonLevels.org provides free EPA radon zone data for all 3,143 counties in the United States. Enter any address, city, or ZIP code to instantly see the EPA radon zone classification for that area, along with testing recommendations and guidance on what your zone means for your home.

The EPA classifies every US county into one of three radon zones based on predicted average indoor radon screening levels. Zone 1 counties have the highest radon potential, with predicted levels above the EPA's 4 pCi/L action level. Zone 2 counties fall between 2 and 4 pCi/L, and Zone 3 counties are below 2 pCi/L. These classifications are based on indoor radon measurements, geology, aerial radioactivity, soil permeability, and foundation type.

Whether you're buying a home, building new construction, or simply want to know the radon risk where you live, start with a free lookup above. Every county page includes testing advice, real estate considerations, new construction guidance, and links to neighboring counties so you can see the broader picture for your area.