In keeping with our ongoing mission to inform communities about the risks of radon exposure indoors, Protect Environmental is releasing its National Radon Risk Index™, which utilizes data from its proprietary National Radon Risk Search™ tool to rank radon risk in communities across the country. This search tool accesses the most comprehensive collection of radon test results in the country, representing more than 2.5 million data points from sources that include the Centers for Disease Control and Prevention (CDC), as well as our own internal testing data. We strongly believe that by empowering communities with important radon risk information, more action will be taken to prevent radon-induced lung cancer in the places we live, work, and learn. The first step in mitigating against the risks of elevated radon levels is to test.
Our index for 2023 is broken into five sections, with each section including a ranking of the top 10 communities. The sections include:
- Highest radon level recorded in a building tested within the community
- Average radon level of buildings tested within the community
- Percentage of buildings tested within the community with a radon level above the EPA action level
- Highest percentage of residential buildings characterized for radon risk within the community
- Lowest percentage of residential buildings characterized for radon risk within the community
Highest radon level recorded in a building tested within the community*
| County, State | Radon Level |
|---|---|
| Dallas County, Texas | 7,879.3 pCi/L |
| Litchfield County, Connecticut | 4,800.0 pCi/L |
| La Plata County, Colorado | 4,115.0 pCi/L |
| Wilkes County, North Carolina | 3,200.0 pCi/L |
| Oakland County, Michigan | 2,297.0 pCi/L |
| Lawrence County, South Dakota | 1,431.3 pCi/L |
| Bucks County, Pennsylvania | 1,398.9 pCi/L |
| Schuylkill County, Pennsylvania | 1,300.0 pCi/L |
| Montgomery County, Maryland | 1,287.1 pCi/L |
| Nevada County, California | 1,100.0 pCi/L |
Average radon level of buildings tested within the community*
| County, State | Radon Level |
|---|---|
| Hinsdale County, Colorado | 53.8 pCi/L |
| Custer County, South Dakota | 30.1 pCi/L |
| Mineral County, Colorado | 29.2 pCi/L |
| Lawrence County, South Dakota | 29.0 pCi/L |
| Knox County, Ohio | 23.6 pCi/L |
| Butte County, Idaho | 21.8 pCi/L |
| Forest County, Pennsylvania | 19.8 pCi/L |
| Mifflin County, Pennsylvania | 19.3 pCi/L |
| Lincoln County, Montana | 19.3 pCi/L |
| Klickitat County, Washington | 18.5 pCi/L |
Percentage of buildings tested within the community with a radon level above the EPA action level *
| County, State | Percentage |
|---|---|
| Roosevelt County, Montana | 93.8% |
| Emmons County, North Dakota | 86.2% |
| Clay County, Nebraska | 85.1% |
| Billing County, North Dakota | 85.0% |
| Sioux County, Iowa | 84.2% |
| Rock County, Minnesota | 83.8% |
| Webster County, Nebraska | 83.2% |
| Pembina County, North Dakota | 82.5% |
| Plymouth County, Iowa | 82.3% |
| Hand County, South Dakota | 81.8% |
Highest percentage of residential buildings characterized for radon risk within the community*
| County, State | Percentage |
|---|---|
| Johnson County, Iowa | 10.974% |
| Adams County, Illinois | 10.267% |
| Washington County, Iowa | 9.805% |
| Wayne County, Nebraska | 9.190% |
| Winnebago County, Iowa | 9.184% |
| Sioux County, Iowa | 9.154% |
| Collier County, Florida | 8.972% |
| Shelby County, Iowa | 8.842% |
| Dubuque County, Iowa | 8.783% |
| Transylvania County, North Carolina | 8.704% |
Lowest percentage of residential buildings characterized for radon risk within the community*
| County, State | Percentage |
|---|---|
| Hildago County, Texas | 0.003% |
| Cameron County, Texas | 0.004% |
| Ellis County, Texas | 0.007% |
| Stanislaus County, California | 0.008% |
| Caddo County, Louisiana | 0.008% |
| Yuma County, Arizona | 0.009% |
| Wichita County, Texas | 0.009% |
| East Baton Rouge County, Louisiana | 0.009% |
| Solano County, California | 0.010% |
| Bay County, Florida | 0.010% |
If you are interested in using the National Radon Risk Index for a news story or other public use, contact our press team or call us at 502-410-5000 for citation information and permitted usage.
*Due to regulations prohibiting the sharing of radon test results, we are unable to provide CDC data for Kansas and New Jersey. New Jersey results are provided using data captured by Protect Environmental. Due to lack of reporting to the CDC, we are unable to provide data for Hawaii and Mississippi.
**The data points utilized for the search tool are county-level. Utilizing the zip code search component returns data for the county or counties where the zip code is located. The mean average was used in calculating the average radon level for buildings tested within a community. Counties with less than 10 test results are not included in the index analysis.
Calculation of the index was based upon analysis of data representing more than 2.5 million data points compiled from the Centers for Disease Control and Prevention (CDC) and Protect Environmental.
- Centers for Disease Control and Prevention. National Environmental Public Health Tracking Network. cdc.gov/ephtracking
Calculation of radiation dose equivalents included with the National Radon Risk Search tool was based upon information obtained through the Agency for Toxic Substances and Disease Registry.
- S. Department of Health and Human Services Public Service, ABDR. Toxicological profile for radon. Atlanta, GA: Agency for Toxic Substances and Disease Registry.
Frequently Asked Questions
The National Radon Risk Index is Protect Environmental ranking of radon risk in communities across the country. It draws on our National Radon Risk Search tool to compare counties by measures such as highest recorded level, average level, and the share of buildings tested above the EPA action level.
The index is built from more than 2.5 million radon data points compiled from the Centers for Disease Control and Prevention and Protect Environmental own testing records. County-level data is analyzed, and counties with fewer than 10 test results are excluded so the rankings reflect meaningful sample sizes.
Not necessarily. Community rankings show broad patterns, but radon levels can vary widely from home to home, even between neighbors on the same street. A high-ranking area is a reason to pay attention, but only a test of your own home tells you its actual radon level.
You can use Protect Environmental National Radon Risk Search tool, which returns radon data for the county or counties where your zip code is located. It is a helpful starting point for understanding local risk, but testing your specific home remains the only way to confirm your level.
The EPA recommends taking action to reduce radon when a home tests at 4.0 picocuries per liter or higher. It is a guideline for when mitigation is advised, not a line between safe and unsafe. Because no level is completely safe, reducing radon as much as possible is wise.
Some states are not fully represented because of reporting rules and data availability. Regulations prevent sharing certain CDC results for Kansas and New Jersey, so New Jersey figures come from Protect Environmental data. Hawaii and Mississippi are not included due to limited reporting to the CDC.
