Predicted radon levels for every US county and ZIP code
Modeled indoor radon estimates for 3,085 counties and 29,215 ZIP codes, plus the EPA radon zone for all 3,143 counties - so you know whether to test, and how urgently.
1.8
pCi/L US predicted basement avg (pop.-weighted)
196
counties predicted ≥ 4 pCi/L
1,071
EPA Zone 1 counties
Check your ZIP code
Predicted (model estimate). The pCi/L figures on this page are long-term area averages from a peer-reviewed national model built on millions of real radon tests (2001-2021). They describe the typical home in this area - not your home, which can be several times higher or lower. The EPA radon zone is a separate, 1993 county-level classification. How the numbers work.
What radon is
A radioactive gas from the natural decay of uranium in soil and rock. It seeps into homes through foundation cracks and sump pits, and it is the leading cause of lung cancer among non-smokers. You cannot see, smell or taste it.
How we grade an area
High = predicted basement average ≥ 4 pCi/L (EPA action level). Moderate = 2-4 (EPA "consider fixing"). Low = below 2. Every page also shows the county's EPA zone and the model's uncertainty.
What to do with it
Use the grade to decide how urgently to test - then test. Read how to test, what mitigation costs and radon in a home sale.
25 highest predicted counties
Population-weighted mean of the model's ZIP-level basement predictions (2001-2021).
| # | County | State | Predicted basement | Grade | EPA zone |
|---|---|---|---|---|---|
| 1 | Sioux County | Iowa | 6.3 pCi/L | High | EPA Zone 1 |
| 2 | Shelby County | Iowa | 6.1 pCi/L | High | EPA Zone 1 |
| 3 | Cherokee County | Iowa | 6.0 pCi/L | High | EPA Zone 1 |
| 4 | Ida County | Iowa | 6.0 pCi/L | High | EPA Zone 1 |
| 5 | Plymouth County | Iowa | 5.9 pCi/L | High | EPA Zone 1 |
| 6 | O'Brien County | Iowa | 5.9 pCi/L | High | EPA Zone 1 |
| 7 | Audubon County | Iowa | 5.9 pCi/L | High | EPA Zone 1 |
| 8 | Knox County | Ohio | 5.8 pCi/L | High | EPA Zone 1 |
| 9 | Licking County | Ohio | 5.8 pCi/L | High | EPA Zone 1 |
| 10 | Burt County | Nebraska | 5.7 pCi/L | High | EPA Zone 1 |
| 11 | Dixon County | Nebraska | 5.6 pCi/L | High | EPA Zone 1 |
| 12 | Buena Vista County | Iowa | 5.5 pCi/L | High | EPA Zone 1 |
| 13 | Lyon County | Iowa | 5.5 pCi/L | High | EPA Zone 1 |
| 14 | Crawford County | Iowa | 5.4 pCi/L | High | EPA Zone 1 |
| 15 | Cass County | Iowa | 5.4 pCi/L | High | EPA Zone 1 |
| 16 | Wayne County | Nebraska | 5.4 pCi/L | High | EPA Zone 1 |
| 17 | Butler County | Nebraska | 5.3 pCi/L | High | EPA Zone 1 |
| 18 | Polk County | Nebraska | 5.3 pCi/L | High | EPA Zone 1 |
| 19 | York County | Nebraska | 5.2 pCi/L | High | EPA Zone 1 |
| 20 | Nemaha County | Nebraska | 5.2 pCi/L | High | EPA Zone 1 |
| 21 | Page County | Iowa | 5.2 pCi/L | High | EPA Zone 1 |
| 22 | Cedar County | Nebraska | 5.2 pCi/L | High | EPA Zone 1 |
| 23 | Montgomery County | Iowa | 5.2 pCi/L | High | EPA Zone 1 |
| 24 | Seward County | Nebraska | 5.2 pCi/L | High | EPA Zone 1 |
| 25 | Jerauld County | South Dakota | 5.2 pCi/L | High | EPA Zone 1 |
Radon by state
Sorted by predicted basement average. Alaska and Hawaii have EPA zones only.
- South Dakota3.9
- Nebraska3.6
- Iowa3.5
- North Dakota3.3
- Montana3.1
- Wyoming3.0
- Ohio2.8
- Idaho2.6
- Colorado2.6
- Kansas2.6
- Kentucky2.5
- Minnesota2.4
- West Virginia2.4
- Tennessee2.3
- Indiana2.3
- Pennsylvania2.3
- Utah2.3
- Missouri2.2
- Maine2.2
- New Mexico2.1
- New Hampshire2.1
- Wisconsin2.0
- Nevada1.9
- Illinois1.9
- Georgia1.9
- Massachusetts1.8
- Alabama1.8
- Oklahoma1.8
- Arkansas1.8
- Arizona1.7
- Oregon1.7
- Vermont1.7
- North Carolina1.7
- Virginia1.6
- South Carolina1.6
- Michigan1.6
- Washington1.6
- Rhode Island1.6
- Texas1.5
- Connecticut1.5
- California1.5
- Mississippi1.5
- Louisiana1.4
- New York1.4
- Delaware1.3
- New Jersey1.3
- Maryland1.3
- Florida1.3
- District of Columbia1.1
- Alaskazones only
- Hawaiizones only
Radon quick answers
- What radon level is dangerous?
- The EPA action level is 4 pCi/L: fix your home at or above it. The EPA also says to consider fixing between 2 and 4 pCi/L, and there is no known safe level - radon is the leading cause of lung cancer among non-smokers. Nationally the model predicts a population-weighted basement average of 1.8 pCi/L, and 1,220 of 29,215 ZIP codes (4.2%) are predicted at or above 4.
- How do I find the radon level in my area?
- Enter your 5-digit ZIP above to see the predicted long-term basement average for your ZIP and a link to your county report with its EPA zone. The number is a modeled estimate for the area; the only way to know your own home is to test it with a short-term kit or a continuous monitor.
- What are EPA radon zones?
- The EPA Map of Radon Zones (1993) puts every county in Zone 1 (predicted average indoor screening level above 4 pCi/L), Zone 2 (2-4) or Zone 3 (below 2). Of 3,143 counties, 1,071 are Zone 1, 1,034 Zone 2 and 1,038 Zone 3. The EPA stresses that homes with high radon exist in all three zones and that the map is not a substitute for testing.
- Which states have the highest radon?
- By population-weighted predicted basement average, the highest states are South Dakota (3.9 pCi/L), Nebraska (3.6 pCi/L), Iowa (3.5 pCi/L), North Dakota (3.3 pCi/L), Montana (3.1 pCi/L). The lowest are Maryland (1.3), Florida (1.3), District of Columbia (1.1). Alaska and Hawaii are not covered by the model, but their counties are shown with EPA zones.
- Should I test even if my area is predicted low?
- Yes. The EPA recommends testing every home below the third floor regardless of zone. Radon depends on the soil directly under a house, how the foundation is built and how the home is ventilated, so neighboring houses commonly differ by several times. A short-term test costs roughly the price of a pizza.
Sources: National Radon Exposure Model (OSF, CC0) and the EPA radon program. See methodology.