Radon in Winnebago County, Illinois
About 4 in 10 homes tested here were at or above the EPA action level.
- Below 2 pCi/L: 29%
- 2 to 4 pCi/L: 27%
- 4 pCi/L or more: 44%
- Median level
- 3.4 pCi/L
- EPA radon zone
- Zone 1
- In Illinois
- 44th of 93
EPA Zone 1, the highest radon potential (predicted average above 4 pCi/L). The EPA zone map dates from 1993 and is meant for planning; high levels are found in every zone.
What to do next
Test your home
Radon levels vary between neighboring houses, so area data can't tell you your own home's level. A short-term test takes 2 to 7 days in the lowest lived-in floor. A long-term test (90 days or more) gives a more reliable average.
If your result is 4 pCi/L or more, fix it
Most homes are fixed with a sub-slab depressurization system: a pipe and a quiet fan that pull radon from under the foundation and vent it above the roof. We're still collecting real installation prices for Illinois.
Use a certified professional
Look for a professional certified by the National Radon Proficiency Program (NRPP) or the National Radon Safety Board (NRSB), or by your state if it certifies radon contractors.
How Winnebago County compares
Share of homes tested at or above 4 pCi/L, with neighboring counties. Lab data 2008–2017, the only source that covers every state.
| Stephenson County | 63% | |
|---|---|---|
| Ogle County | 63% | |
| Rock County, WI | 53% | |
| Green County, WI | 52% | |
| Boone County | 48% | |
| DeKalb County | 46% | |
| Winnebago County | 44% | |
| Illinois | 43% | |
| United States | 36% |
Sources
- EPA Map of Radon Zones (public domain).
- CDC Environmental Public Health Tracking Network, radon tests from labs, 2008–2017. Pre-mitigation tests only.
Last updated October 2026. How we calculate these numbers.