Radon Levels by State: Where Is Radon Most Common?

Some states have serious radon problems. Others... still have radon problems, just not as many people know about it.

The EPA classifies every US county into one of three zones based on predicted average indoor radon levels. Zone 1 is the highest risk -- predicted average above 4.0 pCi/L. Zone 2 falls between 2.0 and 4.0. Zone 3 is below 2.0. But those maps don't tell the whole story.

The Highest-Risk States

Iowa takes the crown. The entire state is Zone 1 -- highest average indoor radon concentration in the country. Not even close.

Pennsylvania is right up there, especially eastern and central PA. The Reading Prong -- a geological formation loaded with uranium-bearing rock -- runs through the Lehigh Valley and extends into New Jersey and New York. If you're in the Philly metro or anywhere in the Lehigh Valley, testing isn't optional. It's essential.

Ohio is mostly Zone 1, particularly the northeastern and central regions. Colorado's Front Range corridor -- Denver, Boulder, Colorado Springs, Fort Collins -- is heavily Zone 1, and Colorado has one of the highest testing rates in the country because of it.

And yeah, Minnesota, Indiana, Nebraska, and the Dakotas all have major Zone 1 coverage. The northern Great Plains got hit hard by glacial deposits that happen to be radon-friendly.

What About the Northeast?

Significant risk across the board. That Reading Prong we mentioned? It's the geological gift that keeps on giving. It runs from Pennsylvania through northern New Jersey, southeastern New York, and into Connecticut. Counties along that formation consistently show elevated levels.

New York, New Jersey, Massachusetts, Connecticut, New Hampshire, Vermont, and Maine all have substantial Zone 1 areas. The Northeast doesn't get as much attention as the Midwest for radon, but it probably should.

The Southeast: Lower on Average, but Don't Get Comfortable

Generally lower levels than up north. But the Appalachian corridor through Virginia, North Carolina, Tennessee, and northern Georgia includes plenty of Zone 1 counties. The piedmont region of the Carolinas also shows elevated levels in spots.

Florida? Lowest average radon levels of any state. But "average" is the operative word -- individual homes can still test high depending on the soil and construction.

Out West

Variable. Colorado and Montana have significant Zone 1 areas. Idaho, Utah, and parts of Washington too. California, Oregon, and the desert Southwest generally run lower, but individual results are all over the map.

So Here's What Actually Matters

Zone maps are county-level predictions. Your home isn't a county -- it's a specific building on specific soil with a specific foundation. Radon levels can vary wildly between neighbors. One house at 1.0 pCi/L, the house next door at 10.0. It happens all the time.

What drives individual home levels:

• Soil composition directly under the foundation
• Foundation condition -- cracks, joints, pipe penetrations
• Building pressure dynamics (stack effect, how your HVAC operates)
• Groundwater radon levels (matters if you're on well water)

This is why the EPA recommends testing ALL homes regardless of zone. A short-term test kit costs $15 to $30. That's nothing compared to the cost of not knowing.

State Testing Programs

A bit of context: many states offer free or discounted radon test kits through their health departments. Some maintain searchable directories of certified testing and mitigation professionals. Check your state environmental agency's website -- or just search for contractors in your state right here.

Look, radon doesn't care about zone maps. It cares about geology and building science. The only way to know your home's actual level is to test it. And if it comes back high, we've got a guide on exactly what to do next.

How EPA Zone Maps and Real Home Tests Work Together

State-level risk discussions are useful, but homeowners need to understand what map data can and cannot do. EPA zone maps classify counties by predicted average potential, not by your exact living room reading. Zone 1 counties are considered higher potential, yet even Zone 2 or Zone 3 areas can produce elevated results in individual houses.

That happens because radon depends on local geology, foundation leakage, and pressure behavior inside each building. Two homes on the same block can test very differently. One may read 1.8 pCi/L while another reads 6.5 pCi/L after weather shifts and HVAC changes.

Best practice is to use state and county risk maps for prioritization, then test your own home to make the actual decision. Start with risk lookup and compare local service availability in cities like Denver and Albany.

States With Moderate Averages Still Produce High Individual Results

Many homeowners assume lower-average states are "safe" and skip testing. That is a costly misunderstanding. Radon is found in every state, and pockets of higher uranium-bearing soil can create elevated indoor readings far from the national high-profile hotspots.

Climate and building operation also matter. During cold seasons, homes are often closed tighter and stack effect intensifies, pulling more soil gas inward. That seasonal pattern is one reason some properties test low in summer but high in winter.

WHO and EPA both emphasize that no level is risk-free. EPA action level remains 4.0 pCi/L, but many families in moderate-risk states still choose mitigation in the 2.0 to 4.0 range when long-term tests stay elevated.

How to Use State Data for a Practical Homeowner Plan

Use a three-step plan. Step 1: identify state and county risk context. Step 2: run a properly placed test in the lowest lived-in level. Step 3: decide on mitigation based on measured result and occupancy pattern. This keeps decisions factual instead of fear-based.

If you are buying, pull state context early so contract language can include testing and repair terms without last-minute conflict. If you are selling, a pre-listing test can reduce surprises and keep negotiations cleaner.

For budgeting, pair your state risk picture with the mitigation cost tool and then compare city-level contractor depth in places like Columbus or Richmond.

Decision Framework 1 for radon levels by state

Homeowners usually get the best outcome when they convert this topic into a step-by-step decision process instead of one big yes-or-no choice. Start with your measured result, confirm testing quality, and then compare options using written scope so every bid can be evaluated fairly.

Use local context to make your plan realistic. Review your state page at state market context, check a comparable city page like local provider depth, and run numbers in the mitigation cost tool. This three-point check helps you avoid overpaying or under-scoping the work.

Technical detail matters here: EPA action level is 4.0 pCi/L, average indoor concentration in U.S. homes is about 1.3 pCi/L, and outdoor background is around 0.4 pCi/L. WHO has also referenced a lower target level near 100 Bq/m3 (about 2.7 pCi/L). Using those benchmarks keeps decisions concrete and consumer-focused.

After you choose a certified professional, set a follow-up testing date immediately. That simple scheduling step is one of the easiest ways to ensure this project actually reduces long-term exposure instead of becoming another unfinished home task.

Field Notes 2: applying this in real homes

Homeowners usually get the best outcome when they convert this topic into a step-by-step decision process instead of one big yes-or-no choice. Start with your measured result, confirm testing quality, and then compare options using written scope so every bid can be evaluated fairly.

Use local context to make your plan realistic. Review your state page at state market context, check a comparable city page like local provider depth, and run numbers in the mitigation cost tool. This three-point check helps you avoid overpaying or under-scoping the work.

Technical detail matters here: EPA action level is 4.0 pCi/L, average indoor concentration in U.S. homes is about 1.3 pCi/L, and outdoor background is around 0.4 pCi/L. WHO has also referenced a lower target level near 100 Bq/m3 (about 2.7 pCi/L). Using those benchmarks keeps decisions concrete and consumer-focused.

After you choose a certified professional, set a follow-up testing date immediately. That simple scheduling step is one of the easiest ways to ensure this project actually reduces long-term exposure instead of becoming another unfinished home task.

FAQ

Can I skip testing if my county is listed lower risk?

No. County categories are broad estimates and cannot predict your specific home result.

Are older homes always higher risk than new homes?

Not always. New homes can have elevated radon too, especially if pressure dynamics and entry pathways are favorable for soil gas movement.

Does finishing a basement reduce radon risk?

Finishing a basement does not remove entry points. It can mask them, which is why testing remains important after renovations.

How often should state-level data influence my decisions?

Use it for planning and urgency, but rely on direct test results in your own home for final action decisions.

Final Planning Checklist for This Topic

If you want one simple approach, do this in order: confirm your latest test quality, compare local options with written scope, choose a certified professional based on outcome plan, and document follow-up testing dates now. This keeps decisions clear and reduces expensive backtracking.

Most homeowners get better results when they set a target outcome before comparing bids. For example, they decide they want a stable long-term result well below 4.0 pCi/L, then ask each contractor to explain how their plan gets there. That shifts the conversation from sales language to measurable performance.

Use your local directories and tools together: review state-level context at Pennsylvania or Colorado, check a comparable city like Anchorage, and run numbers in the mitigation cost tool. Keeping all three views aligned makes your final choice faster and more confident.