Illinois Radon Map, Levels & Testing Guide
Browse the 39 listed county pages surfaced for Illinois. Open a listed county to compare its EPA zone, source caveats, testing meaning, and when mitigation pricing becomes worth checking.
High Risk
Moderate
Low Risk
Official Evidence in Illinois
39 of 39 listed counties have official evidence
Open a county page to see the processed verdict: source confidence, local burden, state percentile, and the next step for no reading, 2.0-3.9, or 4.0+ pCi/L.
100%
covered
Measured
39
State source
39
CDC source
0
Needs source detail
0
Measured Risk Leaders in Illinois
County rankings from actual reported radon tests
These lists rank the visible Illinois county pages by measured radon signals, not by the EPA zone label alone. Use them to spot where the state hub has a real data story before opening individual county pages.
39
measured counties
State-level verdict
This hub has measured high-burden counties, so the first click should be evidence-led.
The state hub is now doing a decision job: it separates first-click counties, retest counties, and lower-signal counties from 39 visible county measurement rows. 36 counties cross the high measured-burden band, so those pages should answer testing and 4.0+ action questions most directly.
First-click counties
Open Knox County first when you need the strongest local answer. It is tagged Test-now from 67.7% 4.0+ - 7.6 pCi/L primary - 1,233 tests. 38 visible measured counties are elevated or high enough to review before lower-signal counties.
Buyer/seller lane
Buyer/seller lane: start with the elevated or high counties, require a fresh lowest-level test, and turn any 4.0+ property result into quote or credit math. The hub has 39 state-source county rows to support that routing.
Retest lane
Retest lane: 2.0-3.9 pCi/L deserves more caution in the elevated/high county set than in lower-signal counties. The hub should send those users to county pages before product or cost paths.
Best county pages to open first
Start with these local evidence pages
Ranked by measured burden, 4.0+ share, test volume, and whether the EPA zone understates the measurement signal.
Knox County
Illinois IEMA-OHS Licensed Radon Measurement Dashboard
67.7% 4.0+ - 7.6 pCi/L primary - 1,233 tests
Knox County is a first-click page: 67.7% of reported tests at or above 4.0 and 7.6 pCi/L primary result. Route no-reading users to a test now and 4.0+ users to quote or credit planning.
Henry County
Illinois IEMA-OHS Licensed Radon Measurement Dashboard
60.3% 4.0+ - 7.0 pCi/L primary - 1,770 tests
Henry County is a first-click page: 60.3% of reported tests at or above 4.0 and 7.0 pCi/L primary result. Route no-reading users to a test now and 4.0+ users to quote or credit planning.
Jo Daviess County
Illinois IEMA-OHS Licensed Radon Measurement Dashboard
52.9% 4.0+ - 7.7 pCi/L primary - 2,026 tests
Jo Daviess County is a first-click page: 52.9% of reported tests at or above 4.0 and 7.7 pCi/L primary result. Route no-reading users to a test now and 4.0+ users to quote or credit planning.
Rock Island County
Illinois IEMA-OHS Licensed Radon Measurement Dashboard
60.2% 4.0+ - 6.3 pCi/L primary - 6,430 tests
Rock Island County is a first-click page: 60.2% of reported tests at or above 4.0 and 6.3 pCi/L primary result. Route no-reading users to a test now and 4.0+ users to quote or credit planning.
Highest 4.0+ share
Primary result 7.6 pCi/L - high-end 19.6 pCi/L
Illinois IEMA-OHS Licensed Radon Measurement Dashboard
Primary result 7.0 pCi/L - high-end 19.3 pCi/L
Illinois IEMA-OHS Licensed Radon Measurement Dashboard
Primary result 6.3 pCi/L - high-end 16.4 pCi/L
Illinois IEMA-OHS Licensed Radon Measurement Dashboard
Primary result 6.6 pCi/L - high-end 16.9 pCi/L
Illinois IEMA-OHS Licensed Radon Measurement Dashboard
Primary result 6.6 pCi/L - high-end 17.7 pCi/L
Illinois IEMA-OHS Licensed Radon Measurement Dashboard
Highest high-end reading
4.0+ share 52.9% - primary result 7.7 pCi/L
Illinois IEMA-OHS Licensed Radon Measurement Dashboard
4.0+ share 55.2% - primary result 6.9 pCi/L
Illinois IEMA-OHS Licensed Radon Measurement Dashboard
4.0+ share 67.7% - primary result 7.6 pCi/L
Illinois IEMA-OHS Licensed Radon Measurement Dashboard
4.0+ share 50.4% - primary result 6.0 pCi/L
Illinois IEMA-OHS Licensed Radon Measurement Dashboard
4.0+ share 54.8% - primary result 6.4 pCi/L
Illinois IEMA-OHS Licensed Radon Measurement Dashboard
Most reported tests
4.0+ share 34.9% - primary result 4.2 pCi/L
Illinois IEMA-OHS Licensed Radon Measurement Dashboard
4.0+ share 20.6% - primary result 2.9 pCi/L
Illinois IEMA-OHS Licensed Radon Measurement Dashboard
4.0+ share 29.2% - primary result 3.6 pCi/L
Illinois IEMA-OHS Licensed Radon Measurement Dashboard
4.0+ share 38.6% - primary result 4.7 pCi/L
Illinois IEMA-OHS Licensed Radon Measurement Dashboard
4.0+ share 38.8% - primary result 4.6 pCi/L
Illinois IEMA-OHS Licensed Radon Measurement Dashboard
Measured pattern
Among 39 visible counties with measurement tables, 36 land in the high measured-burden band and 38 land in high or elevated measured-burden bands. That lets this hub rank counties by observed test distribution instead of repeating the EPA map.
Map vs measurements
6 elevated measured counties are not EPA Zone 1. Those are the pages where the actual test distribution matters more than a map-only answer.
Source confidence
All measured rows shown here use state-specific official sources, so this hub can make source-backed county comparisons without leaning on a national fallback.
Already Tested
View Illinois Cost Estimates
If you already have a radon result, skip the directory and move straight to local price guidance.
Understand the Number
2.0 vs 4.0 vs 8.0 pCi/L
Use the parent levels guide if you need the plain-English meaning of a radon result before browsing counties.
Need a Number First
Read the Testing Guide
Use the fastest valid radon test setup before you compare quotes or ask whether mitigation is worth it.
Browse Counties
Jump to the Directory
Open your county to see its EPA zone, testing meaning, and the point where mitigation becomes worth pricing.
Official State Resource
Illinois radon program and rules
Use the state program link to verify local radon guidance, disclosure language, and contractor credential expectations before you act on an estimate.
Disclosure rule tracked
Illinois requires sellers to disclose known radon test results to buyers under the Residential Real Property Disclosure Act.
State licensing required
Illinois requires radon mitigation professionals to be licensed by the Illinois Emergency Management Agency (IEMA).
Already tested? Get your itemized mitigation cost estimate.
View Illinois Mitigation Cost Estimates ->