2026-06-18 · 7 min read
Top 10 High-Radon Cities in America (2026)
EPA data reveals which U.S. cities have the highest radon levels. Discover whether your metro area is on the list and what to do about it.
Why Are Certain Cities Radioactive?
Radon isn't evenly distributed across America. It concentrates in certain cities for one reason: geology. Cities built on granite (Colorado), glacial deposits (Midwest), Appalachian black shale (Pennsylvania), and other uranium-rich rock have systematically higher radon levels.
The EPA divides the country into three radon potential zones. Zone 1 counties account for 40% of U.S. homes and predict 2.0 pCi/L or higher. Cities in these counties consistently test high.
Here are the 10 U.S. metros with the highest radon levels — and what to do if you live there.
1. Reading / Lancaster, Pennsylvania
Average: 10.2 pCi/L | % exceeding action level: ~35%
The Reading Prong — a belt of uranium-bearing metamorphic rock running through Pennsylvania, New Jersey, and into New York — creates the highest radon concentrations in the continental U.S. Reading and Lancaster sit directly on this formation.
Why it's high: The Reading Prong contains exposed uranium ore and shale. Homes built directly on this rock foundation have radon seeping through constantly.
What to do: Test immediately. If you're buying in this area, make testing a contingency. Mitigation costs $1,500–$3,500 for most homes here.
2. Denver / Boulder, Colorado
Average: 8.9 pCi/L | % exceeding action level: ~21%
The Front Range sits on Precambrian granite bedrock — some of the oldest, most uranium-rich rock in North America. High elevation (5,280 feet in Denver) also makes radon accumulation easier in homes.
Why it's high: Granite geology + elevation + low humidity (radon doesn't dissipate as easily in dry air).
What to do: Most Denver homeowners test as a matter of routine. A mitigation system here typically costs $1,200–$2,500.
3. Des Moines / Cedar Rapids, Iowa
Average: 8.5 pCi/L | % exceeding action level: ~28%
Iowa sits atop glacial till — rock and sediment deposited 20,000 years ago from the Canadian Shield, which is uranium-rich. This covers most of Iowa and creates one of the highest radon averages in the nation.
Why it's high: Glacial geology is uranium-bearing. Sub-slab communication is excellent (loose glacial deposits), so radon travels far underground and enters homes easily.
What to do: Test without delay. Iowa has state-sponsored mitigation rebates up to $2,000, making it cheaper to mitigate here than in most states.
4. Minneapolis-St Paul, Minnesota
Average: 8.3 pCi/L | % exceeding action level: ~27%
Minneapolis radon mitigation →
Like Iowa, Minnesota is glaciated terrain. The Twin Cities sit on a complex mix of glacial deposits and underlying Precambrian granite — both uranium-bearing.
Why it's high: Glacial geology + high water table in some areas (forces radon concentrations higher indoors).
What to do: Testing is standard here. Most contractors quote $1,200–$2,800 for Twin Cities mitigation.
5. Pittsburgh, Pennsylvania
Average: 7.8 pCi/L | % exceeding action level: ~22%
Pittsburgh sits on Appalachian black shale — organic-rich sedimentary rock that contains uranium. The thick coal seams underlying Pittsburgh also concentrate radon in certain pockets.
Why it's high: Black shale geology. Pittsburgh's heavy industrial history also means older foundations (pre-1950) are common, and these tend to have more radon entry points.
What to do: Test, especially if your home was built before 1980. Crawl space mitigation costs $2,500–$4,500 here; slab jobs run $1,000–$2,000.
6. Cleveland / Akron, Ohio
Average: 6.8 pCi/L | % exceeding action level: ~19%
Ohio's northern tier was heavily glaciated. The glacial deposits under Cleveland contain uranium from Canadian Shield rock. Many homes here have crawl spaces (typical for 1950s–1970s construction), which accumulate radon faster than slabs.
Why it's high: Glacial geology + older, more porous foundations.
What to do: Test, particularly if you have a crawl space. Mitigation costs $1,500–$3,500 for slab; $2,500–$5,000 for crawl spaces.
7. Chicago, Illinois
Average: 6.3 pCi/L | % exceeding action level: ~18%
Chicago is built on glacial terrain — mostly clay and silt deposits from the last ice age, mixed with uranium-bearing rock brought south from Canada.
Why it's high: Glacial geology + older housing stock (1920s–1970s homes are common in Chicago, and these have less seal against radon).
What to do: Testing is standard in Chicago real estate. Most homes here mitigate for $1,200–$2,500.
8. Kansas City, Kansas / Missouri
Average: 5.9 pCi/L | % exceeding action level: ~17%
Kansas City sits on the edge of glaciated and non-glaciated terrain. The glacial deposits around the city contain uranium; the underlying bedrock is Precambrian granite and shale.
Why it's high: Transition zone between glacial and non-glacial geology, both uranium-bearing.
What to do: Testing is recommended. Mitigation costs $1,000–$2,500 here.
9. Columbus, Ohio
Average: 5.8 pCi/L | % exceeding action level: ~16%
Columbus sits on glacial outwash — sand, gravel, and fine sediment deposited during ice age melt. This material has excellent sub-slab communication, meaning radon travels far underground.
Why it's high: Glacial geology + excellent radon transport through loose aggregate.
What to do: Testing is standard here. Mitigation costs $1,000–$2,500 for most Columbus homes.
10. Billings, Montana
Average: 5.7 pCi/L | % exceeding action level: ~15%
Billings sits on the edge of extensive Montana uranium deposits — the state was a major uranium mining region during the Cold War. Even though mining has stopped, radon from these deposits seeps through the geology.
Why it's high: Historical uranium geology + mountain elevation.
What to do: Test your home. Mitigation is less common in Montana than in eastern cities, but contractors are available. Expect $1,200–$2,500.
What If Your City Isn't Here?
This list captures the *highest-average* cities, but radon exists everywhere. The EPA recommends testing in all 50 states. Zone 2 and Zone 3 cities still have radon — just lower averages. Individual homes vary widely.
The only way to know your home's radon level is to test.
How to Test in Your City
DIY Short-Term Test (48–72 Hours)
Cost: $25–$50 (kit) + lab fee
Order from our shop. Activate, place in your lowest living area with doors/windows closed, mail to the lab after 2–3 days.
Professional Short-Term Test
Cost: $200–$400
A certified contractor places a continuous radon monitor in your home for 48–72 hours and provides a detailed report.
Long-Term Test (90+ Days)
Cost: $300–$600
More accurate, captures seasonal variation. Recommended for Zone 1 and Zone 2 cities before making mitigation decisions.
If Your Test Comes Back Elevated (4+ pCi/L)
- Schedule a mitigation assessment with a certified contractor — it's usually free or $50–$150
- Get 2–3 quotes — pricing varies 20–40% between contractors
- Check for rebates — many high-radon states offer $500–$2,000 in mitigation rebates
- Schedule installation — most jobs take 4–8 hours
- Retest — 48–96 hours after installation to confirm success
Frequently Asked Questions
Why do certain cities have higher radon than others?
Radon comes from uranium decay in soil and rock. Cities built on uranium-rich geology — granite in Colorado, glacial deposits in the Midwest, black shales in Pennsylvania — accumulate radon. Soil type, home construction, and foundation design also play major roles.
If my city is on this list, do I definitely have radon?
No. Cities with high *average* radon still have individual homes below the EPA action level (4 pCi/L). Two homes in the same city can vary 5–10x. The only way to know your home's level is to test.
What should I do if I live in one of these cities?
Test your home immediately using a short-term radon test kit ($25–$50) or hire a professional ($200–$300). If above 4 pCi/L, get mitigation quotes from certified contractors.
Are high-radon cities more expensive to mitigate?
Not necessarily. Labor costs vary by region (California is expensive; Midwest is cheaper), but radon mitigation pricing is based more on your specific foundation type than on city radon levels.
Find a Certified Mitigator Near You
Every contractor on RadonBase is NRPP or NRSB certified — mitigators only, no testers.
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