Updated November 2026 · Data: EPA Map of Radon Zones · Sources
Radon is a widespread concern in Illinois: 56 of its 102 counties are in EPA Zone 1, the group with the highest predicted indoor radon levels. According to the Illinois Emergency Management Agency (IEMA), 41% of homes tested in Illinois are above 4 pCi/L, the statewide average of tested homes is 4.9 pCi/L, and radon is linked to about 1,200 deaths in the state each year. Find your county below, then learn how to test your home and what to do if the result is high.
Your county’s zone is not your home’s radon level. Homes with high radon are found in every zone. The EPA recommends testing every home, whatever its zone.
Radon zones by county in Illinois
The table lists the EPA radon zone for each of the 102 counties in Illinois. The zone shows the predicted average indoor radon screening level for homes in that county.
| County | EPA zone | Predicted average indoor level |
|---|---|---|
| Adams | Zone 1 | Above 4 pCi/L |
| Alexander | Zone 3 | Below 2 pCi/L |
| Bond | Zone 2 | 2 to 4 pCi/L |
| Boone | Zone 1 | Above 4 pCi/L |
| Brown | Zone 1 | Above 4 pCi/L |
| Bureau | Zone 1 | Above 4 pCi/L |
| Calhoun | Zone 1 | Above 4 pCi/L |
| Carroll | Zone 1 | Above 4 pCi/L |
| Cass | Zone 1 | Above 4 pCi/L |
| Champaign | Zone 1 | Above 4 pCi/L |
| Christian | Zone 2 | 2 to 4 pCi/L |
| Clark | Zone 2 | 2 to 4 pCi/L |
| Clay | Zone 2 | 2 to 4 pCi/L |
| Clinton | Zone 2 | 2 to 4 pCi/L |
| Coles | Zone 1 | Above 4 pCi/L |
| Cook | Zone 2 | 2 to 4 pCi/L |
| Crawford | Zone 2 | 2 to 4 pCi/L |
| Cumberland | Zone 2 | 2 to 4 pCi/L |
| DeKalb | Zone 1 | Above 4 pCi/L |
| De Witt | Zone 1 | Above 4 pCi/L |
| Douglas | Zone 1 | Above 4 pCi/L |
| DuPage | Zone 2 | 2 to 4 pCi/L |
| Edgar | Zone 1 | Above 4 pCi/L |
| Edwards | Zone 2 | 2 to 4 pCi/L |
| Effingham | Zone 2 | 2 to 4 pCi/L |
| Fayette | Zone 2 | 2 to 4 pCi/L |
| Ford | Zone 1 | Above 4 pCi/L |
| Franklin | Zone 2 | 2 to 4 pCi/L |
| Fulton | Zone 1 | Above 4 pCi/L |
| Gallatin | Zone 2 | 2 to 4 pCi/L |
| Greene | Zone 1 | Above 4 pCi/L |
| Grundy | Zone 1 | Above 4 pCi/L |
| Hamilton | Zone 2 | 2 to 4 pCi/L |
| Hancock | Zone 1 | Above 4 pCi/L |
| Hardin | Zone 2 | 2 to 4 pCi/L |
| Henderson | Zone 1 | Above 4 pCi/L |
| Henry | Zone 1 | Above 4 pCi/L |
| Iroquois | Zone 1 | Above 4 pCi/L |
| Jackson | Zone 2 | 2 to 4 pCi/L |
| Jasper | Zone 2 | 2 to 4 pCi/L |
| Jefferson | Zone 2 | 2 to 4 pCi/L |
| Jersey | Zone 1 | Above 4 pCi/L |
| Jo Daviess | Zone 1 | Above 4 pCi/L |
| Johnson | Zone 2 | 2 to 4 pCi/L |
| Kane | Zone 1 | Above 4 pCi/L |
| Kankakee | Zone 2 | 2 to 4 pCi/L |
| Kendall | Zone 1 | Above 4 pCi/L |
| Knox | Zone 1 | Above 4 pCi/L |
| Lake | Zone 2 | 2 to 4 pCi/L |
| LaSalle | Zone 1 | Above 4 pCi/L |
| Lawrence | Zone 2 | 2 to 4 pCi/L |
| Lee | Zone 1 | Above 4 pCi/L |
| Livingston | Zone 1 | Above 4 pCi/L |
| Logan | Zone 1 | Above 4 pCi/L |
| McDonough | Zone 1 | Above 4 pCi/L |
| McHenry | Zone 2 | 2 to 4 pCi/L |
| McLean | Zone 1 | Above 4 pCi/L |
| Macon | Zone 1 | Above 4 pCi/L |
| Macoupin | Zone 2 | 2 to 4 pCi/L |
| Madison | Zone 2 | 2 to 4 pCi/L |
| Marion | Zone 2 | 2 to 4 pCi/L |
| Marshall | Zone 1 | Above 4 pCi/L |
| Mason | Zone 1 | Above 4 pCi/L |
| Massac | Zone 3 | Below 2 pCi/L |
| Menard | Zone 1 | Above 4 pCi/L |
| Mercer | Zone 1 | Above 4 pCi/L |
| Monroe | Zone 2 | 2 to 4 pCi/L |
| Montgomery | Zone 2 | 2 to 4 pCi/L |
| Morgan | Zone 1 | Above 4 pCi/L |
| Moultrie | Zone 1 | Above 4 pCi/L |
| Ogle | Zone 1 | Above 4 pCi/L |
| Peoria | Zone 1 | Above 4 pCi/L |
| Perry | Zone 2 | 2 to 4 pCi/L |
| Piatt | Zone 1 | Above 4 pCi/L |
| Pike | Zone 1 | Above 4 pCi/L |
| Pope | Zone 2 | 2 to 4 pCi/L |
| Pulaski | Zone 3 | Below 2 pCi/L |
| Putnam | Zone 1 | Above 4 pCi/L |
| Randolph | Zone 2 | 2 to 4 pCi/L |
| Richland | Zone 2 | 2 to 4 pCi/L |
| Rock Island | Zone 1 | Above 4 pCi/L |
| St. Clair | Zone 2 | 2 to 4 pCi/L |
| Saline | Zone 2 | 2 to 4 pCi/L |
| Sangamon | Zone 1 | Above 4 pCi/L |
| Schuyler | Zone 1 | Above 4 pCi/L |
| Scott | Zone 1 | Above 4 pCi/L |
| Shelby | Zone 2 | 2 to 4 pCi/L |
| Stark | Zone 1 | Above 4 pCi/L |
| Stephenson | Zone 1 | Above 4 pCi/L |
| Tazewell | Zone 1 | Above 4 pCi/L |
| Union | Zone 2 | 2 to 4 pCi/L |
| Vermilion | Zone 1 | Above 4 pCi/L |
| Wabash | Zone 2 | 2 to 4 pCi/L |
| Warren | Zone 1 | Above 4 pCi/L |
| Washington | Zone 2 | 2 to 4 pCi/L |
| Wayne | Zone 2 | 2 to 4 pCi/L |
| White | Zone 2 | 2 to 4 pCi/L |
| Whiteside | Zone 1 | Above 4 pCi/L |
| Will | Zone 2 | 2 to 4 pCi/L |
| Williamson | Zone 2 | 2 to 4 pCi/L |
| Winnebago | Zone 1 | Above 4 pCi/L |
| Woodford | Zone 1 | Above 4 pCi/L |
What the EPA radon zones mean
- Zone 1 (highest potential): predicted average indoor screening level greater than 4 pCi/L. In Illinois: 56 counties (55%).
- Zone 2 (moderate potential): predicted average between 2 and 4 pCi/L. In Illinois: 43 counties (42%).
- Zone 3 (low potential): predicted average below 2 pCi/L. In Illinois: 3 counties (3%).
The EPA built the map from indoor radon measurements, geology, soil permeability and type of house foundation. It was made to help governments and builders target resources, not to decide whether a single home needs testing.
Illinois counties with the highest radon potential
56 counties in Illinois are in Zone 1: Adams, Boone, Brown, Bureau, Calhoun, Carroll, Cass, Champaign, Coles, DeKalb, De Witt, Douglas, Edgar, Ford, Fulton, Greene, Grundy, Hancock, Henderson, Henry, Iroquois, Jersey, Jo Daviess, Kane, Kendall, Knox, LaSalle, Lee, Livingston, Logan, McDonough, McLean, Macon, Marshall, Mason, Menard, Mercer, Morgan, Moultrie, Ogle, Peoria, Piatt, Pike, Putnam, Rock Island, Sangamon, Schuyler, Scott, Stark, Stephenson, Tazewell, Vermilion, Warren, Whiteside, Winnebago, Woodford.
How to test for radon in Illinois
Testing is the only way to know your home’s radon level. Short-term test kits (2 to 90 days) are sold at hardware stores and online, and some state programs offer kits at low cost; check with the Illinois Emergency Management Agency and Office of Homeland Security (IEMA-OHS), Radon Program. Test in the lowest lived-in level of the home, with windows and doors closed, and follow the kit instructions.
- Do-it-yourself kits: a simple, low-cost first step for your own home.
- Long-term tests (more than 90 days): give a better picture of your home’s year-round average.
- Certified professionals: look for certification from the National Radon Proficiency Program (NRPP) or the National Radon Safety Board (NRSB), and ask the state program whether Illinois requires a state license.
- Buying or selling a home: ask for a radon test as part of the home inspection.
In Illinois, short-term kits sold by county health departments and hardware stores cost about $8 to $15 (Shaw Local, January 2026). Anyone who tests or mitigates radon for others must hold an IEMA license.
If your radon level is high
The EPA recommends fixing your home if the radon level is 4 pCi/L or higher, and considering a fix between 2 and 4 pCi/L. The most common fix is a radon mitigation system (sub-slab depressurization), which pulls radon from under the foundation and vents it outside, above the roof line.
- The EPA says most homes can be fixed for about the same cost as other common home repairs; the price depends on the size and design of the home.
- Get estimates from more than one qualified, certified mitigation contractor. See our radon mitigation cost guide for typical prices.
- Test again after the system is installed, and retest every few years.
Illinois radon program
Radon rules and programs in Illinois
- Licensing: under the Radon Industry Licensing Act (32 Ill. Adm. Code 422), anyone providing radon measurement, mitigation or laboratory services in Illinois must hold a current IEMA license.
- Home sales: under the Illinois Radon Awareness Act, buyers of residential property must receive IEMA’s pamphlet “Radon Testing Guidelines for Real Estate Transactions”, and the parties sign a Disclosure of Information on Radon Hazards stating any known elevated radon level or mitigation system.
- County data: IEMA reports that 73 of Illinois’s 102 counties have an average indoor radon level above 4 pCi/L in tested homes.
Contact
The Illinois Emergency Management Agency and Office of Homeland Security (IEMA-OHS), Radon Program answers questions from residents about radon testing, results and certified professionals.
- Phone: 1-800-325-1245 · 217-782-1325
- Website: iemaohs.illinois.gov/nrs/radon.html
Contact details as listed by the state radon program directory. Please confirm on the program’s website before calling.
Frequently asked questions
How common is radon in Illinois homes?
IEMA data show that 41% of homes tested in Illinois are above the EPA action level of 4 pCi/L, and the average of tested homes is 4.9 pCi/L.
Do radon testers need a license in Illinois?
Yes. Under the Radon Industry Licensing Act, anyone providing radon testing, mitigation or lab services in Illinois must hold an IEMA license.
Is radon a problem in Illinois?
56 of Illinois’s 102 counties are in EPA Zone 1, where the predicted average indoor radon level is above 4 pCi/L, and 43 are in Zone 2 (2 to 4 pCi/L). High levels can be found in any home, so testing is the only way to know.
Which Illinois counties have the highest radon potential?
The 56 counties in EPA Zone 1 have the highest predicted average levels. You can find them in the table above and in the Zone 1 list.
What radon level is safe?
There is no known safe level of radon. The EPA recommends fixing your home at 4 pCi/L or higher and considering a fix between 2 and 4 pCi/L.
Sources
- SOSRadon.org (CRCPD/EPA): Illinois state radon program fact sheet (IEMA data, undated)
- Shaw Local: State says radon gas linked to 1,200 Illinois deaths annually (January 2026)
- U.S. EPA: EPA Map of Radon Zones (county data file, June 2024)
- U.S. EPA: A Citizen’s Guide to Radon (checked November 2026)
- U.S. EPA: How much can a radon mitigation system cost? (updated September 16, 2026)
- Illinois Emergency Management Agency and Office of Homeland Security (IEMA-OHS), Radon Program (checked November 2026)
- SOSRadon.org (CRCPD): State radon contacts (checked November 2026)