Illinois Radon Map, Levels & Testing Guide
Browse the 102 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
102 of 102 listed counties have official evidence
Open a county page to see the official source context: measurement fields, local burden, state percentile, and the next step for no reading, 2.0-3.9, or 4.0+ pCi/L.
100%
covered
Measured
102
State source
100
CDC source
2
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.
102
measured counties
State-level evidence read
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 102 visible county measurement rows. 72 counties cross the high measured-burden band, so those pages should answer testing and 4.0+ action questions most directly.
First-click counties
Open Henderson County first when you need the strongest local answer. It is tagged Test-now from 83.3% 4.0+ - 10.8 pCi/L primary - 24 tests. 85 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 100 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.
Henderson County
Illinois IEMA-OHS Licensed Radon Measurement Dashboard
83.3% 4.0+ - 10.8 pCi/L primary - 24 tests
Henderson County is a first-click page: 83.3% of reported tests at or above 4.0 and 10.8 pCi/L primary result. Route no-reading users to a test now and 4.0+ users to quote or credit planning.
Putnam County
Illinois IEMA-OHS Licensed Radon Measurement Dashboard
73.2% 4.0+ - 10.7 pCi/L primary - 127 tests
Putnam County is a first-click page: 73.2% of reported tests at or above 4.0 and 10.7 pCi/L primary result. Route no-reading users to a test now and 4.0+ users to quote or credit planning.
Carroll County
Illinois IEMA-OHS Licensed Radon Measurement Dashboard
59.9% 4.0+ - 10.2 pCi/L primary - 659 tests
Carroll County is a first-click page: 59.9% of reported tests at or above 4.0 and 10.2 pCi/L primary result. Route no-reading users to a test now and 4.0+ users to quote or credit planning.
Warren County
Illinois IEMA-OHS Licensed Radon Measurement Dashboard
70.3% 4.0+ - 8.6 pCi/L primary - 209 tests
Warren County is a first-click page: 70.3% of reported tests at or above 4.0 and 8.6 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 10.8 pCi/L - high-end 20.6 pCi/L
Illinois IEMA-OHS Licensed Radon Measurement Dashboard
Primary result 10.7 pCi/L - high-end 30.3 pCi/L
Illinois IEMA-OHS Licensed Radon Measurement Dashboard
Primary result 8.6 pCi/L - high-end 22.2 pCi/L
Illinois IEMA-OHS Licensed Radon Measurement Dashboard
Primary result 7.6 pCi/L - high-end 19.6 pCi/L
Illinois IEMA-OHS Licensed Radon Measurement Dashboard
Primary result 5.4 pCi/L - high-end 11.0 pCi/L
CDC Tracking
Highest high-end reading
4.0+ share 59.9% - primary result 10.2 pCi/L
Illinois IEMA-OHS Licensed Radon Measurement Dashboard
4.0+ share 73.2% - primary result 10.7 pCi/L
Illinois IEMA-OHS Licensed Radon Measurement Dashboard
4.0+ share 60.4% - primary result 9.2 pCi/L
Illinois IEMA-OHS Licensed Radon Measurement Dashboard
4.0+ share 62.4% - primary result 8.4 pCi/L
Illinois IEMA-OHS Licensed Radon Measurement Dashboard
4.0+ share 48.6% - primary result 6.2 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 102 visible counties with measurement tables, 72 land in the high measured-burden band and 85 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
29 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 strategy
100 measured counties use state-specific sources and 2 use CDC Tracking. State-specific sources carry the clearest local context; CDC rows remain useful but need peer comparison and home-test decision framing.
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 ->