Radon is a naturally occurring, cancer-causing, radioactive gas that enters buildings from the surrounding soil  It is colorless, odorless, and tasteless.


Radon comes from the natural (radioactive) breakdown of uranium in soil, rock and water and gets into the air you breathe.  Radon can be found all over the United States. 


According to the Surgeon General of the United States, radon is the second leading cause of lung cancer -- second only to smoking.  According to a risk assessment from the Environmental Protection Agency (EPA), radon causes 21,000 premature cancer deaths each year in the United States. 


Southeastern Minnesota and Iowa have some of the highest concentrations of radon in the country.

zone 1 

Highest Potential 

Zone 1 counties have a predicted average indoor radon screening level greater than 4 pCi/L (pico curies per liter) (red zones) 

zone 2 

Moderate Potential

Zone 2 counties have a predicted average indoor radon screening level between 2 and 4 pCi/L (orange zones)

zone 3 

Low Potential

Zone 3 counties have a predicted average indoor radon screening level less than 2 pCi/L (yellow zones)

The purpose of this map is to assist National, State, and local organizations to target their resources and to implement radon-resistant building codes.  This map is not intended to be used to determine if a home in a given zone should be tested for radon.  Homes with elevated levels of radon have been found in all three zones.  All homes should be tested regardless of geographic location.  Important points to note:

  • All homes should test for radon, regardless of geographic location or zone designation.
  • There are many thousands of individual homes with elevated radon levels in Zone 2 and 3.  Elevated levels can be found in Zone 2 and Zone 3 counties.
  • All uses of the map should carefully review the map documentation for information on within-county variations in radon potential and supplement the map with locally available information before making any decisions.
  • The map is not to be used in lieu of testing during real estate transactions.

The map was developed using five factors to determine radon potential:  indoor radon measurement, geology, aerial radioactivity, soil permeability, and foundation type.  Radon potential assessment is based on geologic provinces.  Radon Index Matrix is the quantitative assessment of radon potential.  Confidence Index Matrix shows the quantity and quality of the data used to assess radon potential.  Geologic Provinces were adapted to county boundaries for the Map of Radon Zones.