Radon map of every U.S. county
Every county's EPA radon zone and, where a state has published them, the share of reported tests at or above 4 pCi/L. Search a place or pick a county for its figures, its page and its report.
- counties
- 3,231counties
- with an EPA zone
- 3,138with an EPA zone
- with reported tests
- 2,863with reported tests
Counties are shaded by EPA radon zone, darkest for Zone 1 and palest for Zone 3. The county list under the map holds every county and works from the keyboard.
No county selected.
Reading the map
Two layers, and what neither one is
The map keeps EPA's prediction and the tests already reported apart, because they answer different questions.
PredictedEPA's zone for the whole county
The Predicted layer shades each county by its EPA zone: a prediction of the average indoor screening level across the county, not a figure for any building in it.
- Zone 1Highest predicted potential
- Zone 2Moderate predicted potential
- Zone 3Lower predicted potential
MeasuredTests already reported there
Where a state program has published them, the Measured layer shades each county by the share of reported tests of other buildings at or above 4 pCi/L. Grey means no tests are published for that county.
What radon levels mean- Under 10%
- Under 10%
- 10% to under 25%
- 25% to under 40%
- 40% to under 60%
- 60% or more
- 60% or more
Your home: only a test tells you
Neither layer is a reading of your home. Testing is the only way to know the radon level in a specific building. EPA recommends fixing a home when the radon level is 4 pCi/L or higher.
Which test to use
Radon map by state
Every state’s report has its own zone map, its counties by zone with the highest reported share of tests at or above 4 pCi/L first, and a report for each county. Search the map above by address, county or ZIP code: a ZIP code leads to its county’s report, since radon data is published by county.
Radon map by state: 1 of 51
EPA zones
What the three zones mean
EPA's own words for each zone, and where its predicted average indoor screening level falls on one scale. Zone classifications checked October 19, 2026.
Zone 1: Highest predicted potentialHighest predicted potential
Predicted average indoor screening level greater than 4 pCi/L (greater than 150 Bq/m³)
Zone 2: Moderate predicted potentialModerate predicted potential
Predicted average indoor screening level 2 to 4 pCi/L (75 to 150 Bq/m³)
Zone 3: Lower predicted potentialLower predicted potential
Predicted average indoor screening level less than 2 pCi/L (less than 75 Bq/m³)
A zone is not a measurement
An EPA radon zone describes predicted potential across a whole county. It is not intended to determine whether any individual home should be tested, and homes with elevated levels occur in all three zones. EPA recommends testing every home regardless of zone, and testing is the only way to know the radon level in a specific building.
From the data
The map in numbers
Counted from the EPA zones and the state testing tables behind the map.
- Predicted
1,071
of 3,231 counties are EPA Zone 1, the highest predicted potential (33%).
- Measured
2,863
counties have reported radon tests on file, reported 2005 to 2023.
- Calculated
2
states have every county in Zone 1: Iowa, North Dakota.
Zones by region, the most Zone 1 counties and the spread of reported testsShow the chartsHide the charts
Each bar is every county in that Census region, split by its EPA zone.
- Zone 1
- Zone 2
- Zone 3
- No zone on file
- All counties3,23133% Zone 1
- Northeast21752% Zone 1
- Midwest1,05557% Zone 1
- South1,42213% Zone 1
- West44839% Zone 1
- Territories89No EPA zones
Ranked by the number of counties EPA puts in Zone 1.
The 2,862 counties on the map with a published share, grouped by the map's Measured steps. These are tests of other buildings, never a reading of a home.
- 831 counties,Under 10%
- 447 counties,10% to under 25%
- 536 counties,25% to under 40%
- 632 counties,40% to under 60%
- 416 counties,60% or more
Every state’s counties by zoneShow the tableHide the table
Questions
Questions people ask
Short answers. Each one links to the page with the full answer.
What is radon Zone 1?
Zone 1 is EPA's class for counties with highest predicted potential: a predicted average indoor screening level greater than 4 pCi/L. An EPA radon zone describes predicted potential across a whole county. It is not intended to determine whether any individual home should be tested, and homes with elevated levels occur in all three zones. EPA recommends testing every home regardless of zone, and testing is the only way to know the radon level in a specific building.
What is radon Zone 2?
Zone 2 is EPA's class for counties with moderate predicted potential: a predicted average indoor screening level 2 to 4 pCi/L. An EPA radon zone describes predicted potential across a whole county. It is not intended to determine whether any individual home should be tested, and homes with elevated levels occur in all three zones. EPA recommends testing every home regardless of zone, and testing is the only way to know the radon level in a specific building.
What is radon Zone 3?
Zone 3 is EPA's class for counties with lower predicted potential: a predicted average indoor screening level less than 2 pCi/L. An EPA radon zone describes predicted potential across a whole county. It is not intended to determine whether any individual home should be tested, and homes with elevated levels occur in all three zones. EPA recommends testing every home regardless of zone, and testing is the only way to know the radon level in a specific building.
Where is radon most common?
Radon is most common where the soil and rock carry more uranium, the areas EPA's Map of Radon Zones marks as highest potential, and indoors it is usually highest in basements and ground-contact rooms. Elevated levels have been found in every state and in all three zones, so any home can have a problem.