Radon is the second-leading cause of lung cancer in the United States, responsible for roughly 21,000 deaths each year. The EPA has mapped every county in the country into three risk zones — Zone 1 (high), Zone 2 (moderate), and Zone 3 (low) — based on indoor radon potential. Use the interactive map below to find your county’s zone, explore statewide testing rates, and see which schools are nearby.
Select your state for county-level EPA radon zone data, testing statistics, and state policy information.
What Are EPA Radon Zones?
The EPA’s radon zone map divides all 3,142 U.S. counties into three categories based on predicted average indoor radon screening levels:
- Zone 1 — High (4+ pCi/L): Counties with the highest potential for elevated indoor radon. EPA recommends all homes in Zone 1 counties be tested and mitigated if results exceed 4 pCi/L.
- Zone 2 — Moderate (2-4 pCi/L): Counties with moderate radon potential. Homes here should still be tested — radon levels vary significantly even within a county.
- Zone 3 — Low (below 2 pCi/L): Counties with lowest predicted radon. Testing is still advisable; geology, construction type, and ventilation can push any home above action levels.
These zones were established in 1993 using data from state surveys, geology, housing characteristics, and indoor-measurement studies. They identify where the risk is highest — not where it is absent. The EPA Action Level is 4 pCi/L regardless of zone.
Which States Have the Most Zone 1 Counties?
The highest concentrations of Zone 1 counties are in the northern and central parts of the country, where glacial deposits and uranium-bearing geology drive elevated radon potential. States with a large share of Zone 1 counties include Iowa, Minnesota, Pennsylvania, Ohio, Montana, Idaho, Colorado, and North Dakota. Pennsylvania is notable: nearly all of its counties are classified Zone 1, and the state operates one of the most robust radon testing-and-mitigation programs in the nation.
By contrast, much of the Gulf Coast, Hawaii, and parts of the Southeast sit predominantly in Zone 3, reflecting lower-radon geology.
How to Use This Map
- Click any county to see its EPA radon zone and your state’s testing rate and mitigation policies.
- Search a city or address to jump directly to your location and identify your county’s zone.
- Use My Location to geolocate automatically.
- Toggle schools in the legend to see nearby public and private schools.
- Filter by zone using the legend checkboxes to focus on high-risk, moderate, or low-risk counties.
Schools and Radon Risk
Children spend a significant portion of their day in school buildings, making school radon levels a public health priority. This map overlays NCES school location data so you can see schools alongside county radon zones. Many states now require radon testing in schools — click any school marker to see whether that state mandates testing and has a school-specific radon program in place.
State Radon Programs and Policies
Radon regulation in the United States is primarily managed at the state level. Programs vary considerably: some mandate radon disclosure in real estate transactions, others require new construction to include radon-resistant features, and a growing number require schools to test on a fixed schedule. Click any county to see whether your state has a mandatory disclosure law, a new-construction requirement, a school testing mandate, or a certified-contractor licensing program.
Testing Your Home for Radon
The only way to know your home’s radon level is to test it. Short-term tests (2-7 days) are available at most hardware stores for under $30. Long-term tests (90+ days) provide a more accurate annual average. If your result is at or above 4 pCi/L, EPA recommends mitigation — typically a sub-slab depressurization system that vents radon from beneath the foundation to the outside. Average mitigation cost is $800-$2,500.
Data Sources
County-level radon zone boundaries come from the EPA Map of Radon Zones, served via the EPA’s public ArcGIS MapServer. State testing rates, disclosure laws, new-construction requirements, and school-testing mandates are sourced from AARST state program data. School locations are drawn from the NCES EDGE dataset (public and private schools).
