Radon Map of the United States: EPA Zones by County

Radon is a colourless, odourless radioactive gas that seeps out of the ground and collects indoors. It is the second leading cause of lung cancer in the United States after smoking, and you cannot see, smell or taste it. The map below shows the EPA radon zone for every US county, so you can check your address in a couple of seconds.

One thing to know before you start, because most radon maps online will not tell you: the EPA Map of Radon Zones was drawn in 1993, and it predicts an average for a whole county. It was built to help states and builders target their resources, not to tell any individual household what is happening under their own floor. The EPA is direct about this. Its guidance says the map “should not be used to determine if individual homes need to be tested.”

So this tool gives you two honest layers rather than one false answer. You get the EPA zone for your county, which is what building codes and state programs reference, and you get the USGS geologic radon potential for the exact point you searched, because radon comes out of the ground and geology does not follow county lines. Both are free, official, federal datasets. Neither can tell you your home’s radon level. Only a test can do that.

How to use it

1. Type your address, city or ZIP code into the search box, or tap Use my location to let the map find you.
2. Read the card on the right. It shows your county, its EPA radon zone, and what that zone actually predicts.
3. Check the geology line underneath. This is the USGS geologic radon potential at the precise point you searched, which can differ from the county-wide zone.
4. Tap Show geology layer to see the geologic areas drawn on the map. This is where you can see radon potential changing inside a single county.
5. Tap any county on the map to check it, and use Share to copy a link back to whatever you were looking at.

What the radon zones mean

The EPA sorted every US county into one of three zones based on the average indoor radon screening level it predicted for that county. The zones describe a prediction for the county as a whole. They are not a measurement, and they are not a verdict on your house.

Zone	Predicted county average	What it means in practice
Zone 1	Above 4 pCi/L	Highest predicted potential. Many homes here test above the action level, though plenty test low.
Zone 2	Between 2 and 4 pCi/L	Moderate predicted potential. Homes above the action level are common.
Zone 3	Below 2 pCi/L	Lowest predicted potential. This is not an all-clear. Homes in Zone 3 counties do test high.

Notice that the recommended action is the same in all three rows: test your home. That is not us hedging. It is the EPA’s position, and it is the only conclusion a 1993 county-level prediction can honestly support.

About the data

Two federal datasets sit behind this map, and both are older than most people assume.

• EPA Map of Radon Zones (1993). County zones 1, 2 and 3 for 3,141 counties across the 50 states and DC: 1,068 in Zone 1, 1,035 in Zone 2 and 1,038 in Zone 3. This dataset is static and is not being updated.
• USGS Geologic Radon Potential. 1,031 geologic areas scored by Radon Index, a composite of geology, soil permeability, aerial gamma radioactivity, home architecture and screening radon data. It was published as a national GIS layer in 2025, but that is the digitization date: the underlying assessment is USGS Open-File Report 93-292, also from the early 1990s. We would rather say that plainly than dress a 1993 study up as new.
• County boundaries. US Census TIGER, current, joined to the zones by FIPS code.

Honest limitations. The EPA map covers the 50 states and DC only, so US territories including Puerto Rico, Guam and the US Virgin Islands have no zone. Because the map is from 1993, a handful of places have shifted underneath it: Broomfield County, Colorado was created in 2001 and was never assigned a zone at all, and counties that were renamed since, such as Miami-Dade in Florida and Oglala Lakota in South Dakota, are shown here under their current names carrying the zone from their old ones. Zones stop at county lines, which are administrative boundaries that the geology pays no attention to.

Important: what this map cannot tell you

This map shows the EPA’s 1993 predicted radon zones and USGS geologic radon potential. It is informational, it is not medical advice, and it cannot tell you the radon level in any specific building. The EPA’s own guidance is that the Map of Radon Zones “should not be used to determine if individual homes need to be tested.” Radon levels vary house by house, even between neighbours in the same zone, because they depend on your soil, your foundation, how your home was built and how it is ventilated. Homes in every zone, including Zone 3, can have radon above the EPA action level of 4 pCi/L. The only way to know your level is to test. Testing is inexpensive and the EPA recommends it for every home.

Frequently asked questions

What is a radon zone?

It is the EPA’s 1993 prediction of the average indoor radon screening level across a whole county, expressed as Zone 1 (highest, predicted above 4 pCi/L), Zone 2 (2 to 4 pCi/L) or Zone 3 (lowest, below 2 pCi/L). It was designed so that states, builders and code officials could target radon-resistant construction and outreach where it would do the most good.

Does Zone 3 mean my home is safe?

No. This is the single most common misreading of the map. Zone 3 means the EPA predicted a county average below 2 pCi/L in 1993. Averages hide the individual cases, and homes in Zone 3 counties do test above the action level. Your neighbour can test low while you test high, because radon depends on the ground under your specific foundation and how your specific house is built and ventilated. Zone 3 lowers the odds. It does not answer the question.

How accurate and how fresh is this data?

It is accurate as a reproduction of the official federal datasets, and those datasets are from 1993. That is not a flaw in this map, it is the state of the public data: the EPA Map of Radon Zones has not been redrawn, and the USGS geologic layer published in 2025 is a digitization of a 1993 assessment. Treat both as a guide to what the ground is likely to do in your area, not as a current measurement of your home. Any site presenting this data as today’s radon risk is overselling it.

What is a safe radon level?

The EPA’s action level is 4 pCi/L: at or above that, it recommends fixing your home. Between 2 and 4 pCi/L it suggests you consider fixing it. There is no level that is known to be completely without risk, and the average outdoor level is around 0.4 pCi/L. Mitigation is a well established piece of work, usually a vent pipe and fan system that draws radon from below the foundation and releases it outside.

How do I test for radon?

Short-term test kits sit in the lowest lived-in level of your home for a few days and go to a lab. Long-term kits stay for more than 90 days and give a better picture, because radon swings with season, weather and how much you have the windows open. Many state radon programs offer free or discounted kits, and your state’s radon contact is the place to start. If you are buying a house, a radon test is a standard part of the inspection.

Why does my county have no zone?

Two reasons, both down to the map’s age and scope. US territories were never included, so Puerto Rico, Guam, the US Virgin Islands, American Samoa and the Northern Mariana Islands have no zone. And Broomfield County, Colorado did not exist when the map was drawn: it was carved out of four neighbouring counties in 2001, eight years too late to be assigned one.

What is the difference between the EPA zone and the USGS geologic potential?

The EPA zone is assigned to a whole county and is the number that codes and state programs point at. The USGS geologic radon potential is mapped to geologic areas instead, so it follows rock and soil rather than administrative borders. That is why it is worth looking at both: the geology layer can show potential changing across a single county, which a county-wide zone cannot. They run on the same 1 to 3 scale, where 1 is the highest potential in both.

Where does this data come from, and can I use it?

The zones come from the EPA Map of Radon Zones and the geology from the USGS Geologic Radon Potential layer, both works of the US federal government and in the public domain. County boundaries are US Census TIGER and the basemap is OpenFreeMap with OpenStreetMap contributors. If you use this map, a link back to this page is appreciated.