Radon in Illinois
About 4 in 10 homes tested in Illinois were at or above the EPA action level of 4 pCi/L.
- Below 2 pCi/L: 31%
- 2 to 4 pCi/L: 25%
- 4 pCi/L or more: 43%
The EPA puts 56 of Illinois's 102 counties in Zone 1, its highest radon category, 43 in Zone 2 and 3 in Zone 3.
Every county in Illinois
Sorted by the share of homes tested at or above 4 pCi/L. Select a county for local details and costs.
"–" means fewer than 20 tests or no lab data, too few for a reliable figure.
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.