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Locations and reportsRadon by location

Radon in the United States

A report for every state and county: what EPA predicts for the area and what the radon tests reported to CDC show, each figure with its source.

56 states and territories · 3,231 counties · Reported testing 2014 to 2023

United States, Choose a state

Radon reports by state

Click a state on the map, find it by name, or open a region. Each state shows how many of its counties EPA places in Zone 1, the highest predicted potential.

Skip the mapAlabamaAlaskaArizonaArkansasCaliforniaColoradoConnecticutDelawareDistrict of ColumbiaFloridaGeorgiaHawaiiIdahoIllinoisIndianaIowaKansasKentuckyLouisianaMaineMarylandMassachusettsMichiganMinnesotaMississippiMissouriMontanaNebraskaNevadaNew HampshireNew JerseyNew MexicoNew YorkNorth CarolinaNorth DakotaOhioOklahomaOregonPennsylvaniaRhode IslandSouth CarolinaSouth DakotaTennesseeTexasUtahVermontVirginiaWashingtonWest VirginiaWisconsinWyomingPuerto RicoU.S. Virgin Islands

Choose a state on the map, or find it by name. State outlines: U.S. Census Bureau cartographic boundary files.

Northeast9Midwest12South17West13Territories5

Northeast

Midwest

South

West

Territories

United States, National figures

The national picture

The predicted zones and the reported tests, in separate boxes because they are different kinds of number, with what Radon411 holds beside them.

Predicted potential

1,071 counties in Zone 1

EPA sorts every U.S. county into Zone 1, 2 or 3 by its predicted average indoor screening level.

  • Zone 1: Highest predicted potentialgreater than 4 pCi/L1,071 of 3,231 counties · 33.1%
  • Zone 2: Moderate predicted potential2 to 4 pCi/L1,034 of 3,231 counties · 32.0%
  • Zone 3: Lower predicted potentialless than 2 pCi/L1,033 of 3,231 counties · 32.0%
  • No zone on file93 of 3,231 counties · 2.9%

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.

Predicted: EPA Map of Radon Zones

Reported measurements

Radon tests reported to CDC

Buildings tested
Not available
At or above 4 pCi/L
Not available
Median result
Not available

Tested buildings, not any one home. People testing before a sale, or because they suspect a problem, are over-represented in any reported testing data.

What Radon411 holds

3,231 county reports

Counties with an EPA zone
3,138 of 3,231
Counties with CDC statistics
2,862 of 3,231
State programs checked
50 of 51
Professional listings
1,322

Coverage counts, not radon figures: how many places carry each layer, so you can see where a report is thin.

United States, Zone 1 by state

Where the Zone 1 counties are

Two ways to count the states with the most counties in EPA's highest predicted zone. A county's zone is a prediction for the area, never a reading of any building.

Calculated by Radon411From each county’s published EPA zone

Most Zone 1 counties

Counted by Radon411: the counties in each state whose published EPA zone is Zone 1. States with more counties can rank higher on count alone.

  1. 1Iowa99 of 99
  2. 2Minnesota68 of 87
  3. 3Kansas65 of 105
  4. 4Virginia62 of 133
  5. 5Indiana57 of 92
  6. 6Illinois56 of 102
  7. 7Colorado53 of 64
  8. 7Nebraska53 of 93
  9. 7North Dakota53 of 53
  10. 7Ohio53 of 88
The other 28 states with a Zone 1 county
  1. 11Montana49 of 56
  2. 11Pennsylvania49 of 67
  3. 13South Dakota48 of 66
  4. 14Tennessee39 of 95
  5. 15New York34 of 62
  6. 16Kentucky30 of 120
  7. 17Wisconsin28 of 72
  8. 18Wyoming21 of 23
  9. 19West Virginia20 of 55
  10. 20Idaho19 of 44
  11. 21Alabama13 of 67
  12. 22Maine12 of 16
  13. 23Missouri11 of 115
  14. 24Michigan9 of 83
  15. 24Nevada9 of 17
  16. 26Maryland8 of 24
  17. 26North Carolina8 of 100
  18. 28New Jersey7 of 21
  19. 28New Mexico7 of 33
  20. 28Utah7 of 29
  21. 28Washington7 of 39
  22. 32Connecticut4 of 8
  23. 32Georgia4 of 159
  24. 34Massachusetts3 of 14
  25. 35California2 of 58
  26. 35Rhode Island2 of 5
  27. 37New Hampshire1 of 10
  28. 37South Carolina1 of 46

Highest share of counties in Zone 1

Calculated by Radon411: Zone 1 counties divided by the state's counties with an EPA zone on file. It is a share of counties, not of land, people or homes.

  1. 1Iowa100% (99 of 99)
  2. 1North Dakota100% (53 of 53)
  3. 3Wyoming91% (21 of 23)
  4. 4Montana88% (49 of 56)
  5. 5Colorado83% (53 of 64)
  6. 6Minnesota78% (68 of 87)
  7. 7Maine75% (12 of 16)
  8. 8Pennsylvania73% (49 of 67)
  9. 9South Dakota73% (48 of 66)
  10. 10Indiana62% (57 of 92)
The other 28 states with a Zone 1 county
  1. 11Kansas62% (65 of 105)
  2. 12Ohio60% (53 of 88)
  3. 13Nebraska57% (53 of 93)
  4. 14Illinois55% (56 of 102)
  5. 15New York55% (34 of 62)
  6. 16Nevada53% (9 of 17)
  7. 17Connecticut50% (4 of 8)
  8. 18Virginia47% (62 of 133)
  9. 19Idaho43% (19 of 44)
  10. 20Tennessee41% (39 of 95)
  11. 21Rhode Island40% (2 of 5)
  12. 22Wisconsin39% (28 of 72)
  13. 23West Virginia36% (20 of 55)
  14. 24Maryland33% (8 of 24)
  15. 24New Jersey33% (7 of 21)
  16. 26Kentucky25% (30 of 120)
  17. 27Utah24% (7 of 29)
  18. 28Massachusetts21% (3 of 14)
  19. 29New Mexico21% (7 of 33)
  20. 30Alabama19% (13 of 67)
  21. 31Washington18% (7 of 39)
  22. 32Michigan11% (9 of 83)
  23. 33New Hampshire10% (1 of 10)
  24. 34Missouri10% (11 of 115)
  25. 35North Carolina8% (8 of 100)
  26. 36California3% (2 of 58)
  27. 37Georgia3% (4 of 159)
  28. 38South Carolina2% (1 of 46)

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. How Radon411 calculates

United States, Questions

What radon is, brieflyThe gas, the unit, and EPA's two levels

Radon is a colorless, odorless radioactive gas produced by the decay of uranium in rock and soil. It moves through the ground and enters buildings through cracks in slabs and foundations, sump openings, crawl spaces and service penetrations, where it can accumulate in indoor air.

EPA measures indoor radon in picocuries per liter (pCi/L); the international unit is becquerels per cubic meter (Bq/m³), and 1 pCi/L is about 37 Bq/m³. EPA recommends fixing a home when the radon level is 4 pCi/L or higher. EPA recommends considering a fix when the level is between 2 and 4 pCi/L.

Testing is the only way to know the radon level in a specific building. Nothing on this site measures a specific building, and Radon411 publishes no risk score of its own.

Common questions5 questions about zones, coverage and where to start

What is a radon zone?

EPA’s Map of Radon Zones sorts every U.S. county into Zone 1, 2 or 3 by the predicted average indoor radon screening level for that county. It is a prediction for an area, produced from geology, soil, indoor surveys and building types. EPA states that it is not intended to determine whether an individual home should be tested, and that homes with elevated radon are found in all three zones.

Does a low radon zone mean my home is safe?

No. Zone 3 is the lowest predicted potential, not an all clear. Individual homes with elevated radon occur in every zone, because the level inside a building depends on that building. Testing is the only way to know the radon level in a specific building.

How much radon data does Radon411 have right now?

Radon411 holds real geography for 3,231 counties. 3,138 of them currently have an EPA radon zone published here and 2,862 have CDC reported testing statistics. Counties without a layer show that plainly rather than showing a zero.

Why does Radon411 not publish a single radon risk score?

Because it would blend a prediction for an area with measurements of other people’s buildings and present the result as a fact about yours. We publish the underlying figures, each labelled with where it came from, and we document every derived measure in our methodology.

Where do I start if I have never tested?

With a test kit and the lowest level of the building that people actually use. How to test a home walks through placement and timing, and free and low-cost kits covers the state programmes that distribute them below retail price.

What these figures mean if you own, buy, sell or rent

The zone counts on this page describe counties across the United States. They are predictions for areas, and none of them measures your building.

  • If you own your home

    Test the lowest lived-in level; a short-term kit screens in days, a long-term kit reflects the year.

    How to test a home

  • If you are buying

    Ask for past results and any system's post-mitigation test, and test during the sale.

    Buying a house: radon guide

  • If you are selling

    Testing before you list puts the timing in your hands; disclosure rules differ by state.

    Selling a house: radon guide

  • If you rent, or rent out a home

    A tenant can test; a fix is the owner's to make, and duties differ by state.

    Radon in rental homes
Data coverage by stateHow many of each state's counties carry each radon data layer, as a sortable table
States and territories, with how many of their counties currently have each radon data layer loaded
AlabamaRegion 46767 of 6765 of 67
AlaskaRegion 102925 of 2925 of 29
American SamoaRegion 930 of 30 of 3
ArizonaRegion 91515 of 1513 of 15
ArkansasRegion 67575 of 7561 of 75
CaliforniaRegion 95858 of 5856 of 58
ColoradoRegion 86464 of 6464 of 64
ConnecticutRegion 188 of 88 of 8
DelawareRegion 333 of 33 of 3
District of ColumbiaRegion 311 of 11 of 1
FloridaRegion 46767 of 6765 of 67
GeorgiaRegion 4159159 of 159139 of 159
GuamRegion 910 of 10 of 1
HawaiiRegion 955 of 50 of 5
IdahoRegion 104444 of 4444 of 44
IllinoisRegion 5102102 of 102102 of 102
IndianaRegion 59292 of 9292 of 92
IowaRegion 79999 of 9999 of 99
KansasRegion 7105105 of 105104 of 105
KentuckyRegion 4120120 of 120120 of 120
LouisianaRegion 66464 of 6454 of 64
MaineRegion 11616 of 1616 of 16
MarylandRegion 32424 of 2424 of 24
MassachusettsRegion 11414 of 1414 of 14
MichiganRegion 58383 of 8383 of 83
MinnesotaRegion 58787 of 8787 of 87
MississippiRegion 48282 of 820 of 82
MissouriRegion 7115115 of 115115 of 115
MontanaRegion 85656 of 5653 of 56
NebraskaRegion 79393 of 9393 of 93
NevadaRegion 91717 of 1716 of 17
New HampshireRegion 11010 of 1010 of 10
New JerseyRegion 22121 of 2121 of 21
New MexicoRegion 63333 of 3330 of 33
New YorkRegion 26262 of 6262 of 62
North CarolinaRegion 4100100 of 100100 of 100
North DakotaRegion 85353 of 5353 of 53
Northern Mariana IslandsRegion 940 of 40 of 4
OhioRegion 58888 of 8888 of 88
OklahomaRegion 67777 of 7755 of 77
OregonRegion 103636 of 3636 of 36
PennsylvaniaRegion 36767 of 6767 of 67
Puerto RicoRegion 2780 of 780 of 78
Rhode IslandRegion 155 of 55 of 5
South CarolinaRegion 44646 of 4646 of 46
South DakotaRegion 86666 of 6664 of 66
TennesseeRegion 49595 of 9595 of 95
TexasRegion 6254254 of 254150 of 254
U.S. Virgin IslandsRegion 230 of 30 of 3
UtahRegion 82929 of 2929 of 29
VermontRegion 11414 of 1414 of 14
VirginiaRegion 3133133 of 133132 of 133
WashingtonRegion 103939 of 3939 of 39
West VirginiaRegion 35555 of 5555 of 55
WisconsinRegion 57272 of 7272 of 72
WyomingRegion 82323 of 2323 of 23

United States / Next steps

What to do next