Radon Levels by State: Is Your Home at Risk?

You've probably heard that some states have a radon problem. Maybe you just moved, or you're buying a home in a new area. The question is: does where you live actually determine whether radon is a threat to your house?

The short answer is no—not completely. While geographic location matters, radon doesn't follow state borders. Your county matters more. Your foundation matters more. How tight your basement seal is matters more than the zip code on your address.

This guide walks you through the EPA's radon zone system, shows you which states struggle most with radon, and explains why you shouldn't skip testing just because you live in a "low-risk" area.

Understanding EPA Radon Zones

The EPA's radon classification system splits the country into three potential zones, based on geological surveys and historical radon measurements. Think of these zones as statistical predictions—not absolute rules.

Zone 1: Highest Radon Potential

Zone 1 counties have an average screening level of 4 pCi/L (picocuries per liter) or higher. This is the EPA's action level—if your home measures at 4 pCi/L or above, you need to take mitigation steps. But even in Zone 1, not every house is dangerous. Radon concentrates in certain foundations and soil conditions.

Zone 2: Moderate Radon Potential

Zone 2 averages between 2–4 pCi/L. Homes here should still be tested, as some will exceed the action level. Many states have counties split between Zone 1 and Zone 2, meaning your neighbor's risk might differ from yours.

Zone 3: Lower Radon Potential

Zone 3 averages below 2 pCi/L. These areas are considered lower risk, but the word "lower" is key. Testing is still recommended by the EPA, because radon pockets exist everywhere.

Which States Have the Highest Radon Levels?

The EPA publishes county-level radon data, and when you aggregate it by state, a clear picture emerges. These states contain the most counties in Zone 1:

• Iowa — Nearly the entire state sits in Zone 1, particularly the northern regions. Iowa's glacial geology and certain bedrock formations create ideal conditions for radon migration into homes.
• Pennsylvania — Especially the central and western portions. Pennsylvania's proximity to radon-producing rock formations contributes to widespread household radon.
• Kentucky — Large swaths of the state, particularly eastern mountainous regions, show high radon potential.
• Montana — Western Montana and regions with granite bedrock have elevated radon levels.
• Ohio — Parts of central and eastern Ohio rank in Zone 1, with significant variability across counties.
• South Dakota — Northern and western areas show consistent Zone 1 classification.

Other states with notable Zone 1 pockets include Wyoming, Minnesota, Kansas, Nebraska, and Connecticut. However, these high-risk designations can mask variation. A Zone 1 county might have homes that test above 4 pCi/L and others that test below 2 pCi/L, sometimes on the same street.

Radon Risk by State: Quick Reference

This table shows the predominant EPA zone classification for select U.S. states and their general radon concern level:

Why Your EPA Zone Doesn't Guarantee Your Home's Radon Level

Here's the critical insight that many homeowners miss: living in a Zone 3 (low-risk) county doesn't mean your house is safe from radon. Conversely, a Zone 1 designation doesn't guarantee your home will test high.

Radon Variability at the House Level

Radon concentration depends on:

• Foundation type and condition — Concrete slabs with cracks, gaps in the rim joist, or unsealed pores act like radon funnels. A newer, well-sealed foundation may trap less radon even in a high-risk area.
• Soil and bedrock composition — Your property's specific geology matters. Two houses separated by a mile can sit on different rock formations with vastly different radon potential.
• Home pressure dynamics — Negative indoor air pressure (created by furnaces, exhaust fans, or weather changes) pulls radon from soil into your home. A well-ventilated or pressurized house resists radon entry.
• Depth and drainage — Homes with deeper foundations and good surface drainage typically accumulate less radon.
• Season and weather — Radon levels fluctuate with temperature, humidity, and barometric pressure. Winter often brings higher indoor radon in cold climates.

The EPA has documented homes in Zone 3 counties testing above 4 pCi/L, and homes in Zone 1 counties testing below 2 pCi/L. This is why testing your specific home is the only way to know your actual risk.

Testing for Radon: Next Steps

If you haven't tested your home, start now. The EPA recommends all homes be tested at least once. If you're buying a home or selling one, radon testing is standard practice in most real estate transactions.

Testing Methods

You have two main options:

• Short-term tests — Run 2 to 7 days and give a quick snapshot. Useful for initial screening but affected by weather and seasonal variation.
• Long-term tests — Run 90 days or longer and provide a more accurate picture of your average annual radon exposure. This is the EPA's preferred method.

For guidance on choosing the right test kit for your situation, see our guide on which radon test kit to buy . You can also hire a certified radon inspector to conduct professional testing, though at-home kits are affordable and reliable.

If you want to learn how to test for radon properly—placement, timing, and interpretation—our detailed guide walks you through the process step by step.

What to Do If Your Home Tests High

If your test result is 4 pCi/L or higher, don't panic. Radon is manageable. The EPA and Surgeon General recommend fixing your home if it tests above 4 pCi/L.

The most effective solution is sub-slab depressurization, which vents radon from beneath your foundation. Other strategies include