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Radon Map by County: EPA Radon Zones

Which counties are in the EPA's highest radon zone, where homes are most likely to have high radon.

In 2 states every county is in EPA Zone 1, the highest predicted radon: Iowa, North Dakota. Nationwide, 1,074 of 3,144 counties are Zone 1.

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1,074counties in Zone 1, the highest radon zone
1,032in Zone 2 (moderate)
1,038in Zone 3 (low)
Radon potential (EPA zones) on the Map the Block map of the United StatesOpen the live map →

☢️Share of counties in Zone 1, by state

Iowa99 of 99
North Dakota53 of 53
Wyoming21 of 23
Montana49 of 56
Colorado53 of 64
Minnesota68 of 87
Maine12 of 16
Pennsylvania49 of 67
South Dakota48 of 66
Connecticut6 of 9
Indiana57 of 92
Kansas65 of 105

🔎About this data

EPA's county radon zones from its 1993 map: Zone 1 counties have the highest predicted average indoor radon. Any home can have high radon, whatever the zone; the only way to know is to test.

Source: U.S. EPA Map of Radon Zones (county list re-posted June 2024)

Coverage: 50 states + DC (not Puerto Rico)

How it was checked: All 99 Iowa counties are Zone 1, as Iowa's health department says; zone totals (1,074 / 1,032 / 1,038) are within 0.2% of EPA's list after matching names to today's counties.

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💬Questions and answers

Which states have the most radon?

In 2 states every county is in EPA Zone 1, the highest predicted radon: Iowa, North Dakota. Nationwide, 1,074 of 3,144 counties are Zone 1.

Does a low radon zone mean my home is safe?

No. EPA zones predict county averages; any home can have high radon whatever the zone. The only way to know is to test your home.

Where does this data come from?

U.S. EPA Map of Radon Zones (county list re-posted June 2024). Coverage: 50 states + DC (not Puerto Rico).

Is the map free to use?

Yes. Map the Block is free, with no ads or paywall. You may quote figures with credit to Map the Block (maptheblock.com); for bulk or commercial use there is a Data API.

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Numbers computed from the live map data on October 18, 2026. Free to quote with credit to “Map the Block (maptheblock.com)”; see reuse terms.