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Radon Levels by State (PA, MN, IL)
Radon varies by county and by house, so EPA says to test every home. In Pennsylvania, DEP reports about 40% of tested homes are above 4 pCi/L. Minnesota’s health department estimates 2 in 5 homes exceed 4 pCi/L. EPA’s zone map puts 56 Illinois counties in Zone 1, its highest-potential zone.
| State | Reported indoor levels | EPA zones (counties in Zone 1 / 2 / 3) |
|---|---|---|
| Pennsylvania | About 40% of tested homes above 4 pCi/L (PA DEP) | 49 / 17 / 1 |
| Minnesota | MDH estimates 2 in 5 homes exceed 4.0 pCi/L; 36.2% of properties tested 2016–2025 were at or above 4 pCi/L; state average about 4 pCi/L vs. 1.3 US | 68 / 19 / 0 |
| Illinois | No statewide percentage shown here; we haven’t found an official figure to cite yet | 56 / 43 / 3 |
EPA zones (1993 map): Zone 1 counties have a predicted average indoor screening level above 4 pCi/L, Zone 2 between 2 and 4, Zone 3 below 2. EPA warns the map should not be used to decide whether to test, because high levels are found in all three zones. We cover these three states only so far.
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FAQ
Which zone is my county in?
Check EPA’s Map of Radon Zones; our local contractor pages show the zone for Pennsylvania counties.
Does a low zone mean I don’t need to test?
No. EPA says homes with elevated radon have been found in all three zones and all homes should be tested.