Illinois radon map, by ZIP code
Illinois records every radon measurement its licensed testers submit, and publishes them. That is 498,825 valid home tests. It is one of the largest sets of real radon readings published anywhere, and it is detailed enough to say something honest about an individual ZIP code rather than only about a county or a state.
498,825
recorded by licensed Illinois testers
2.8 pCi/L
across every test in the set
35.8%
the EPA action level
1,118
636 with enough tests to colour
Read this before you use a number from this map
Illinois keeps only the highest reading recorded at each address. That is the state's own rule, not ours. It means every figure on this page runs a little hot, because a house tested three times contributes only its worst result. We publish medians rather than averages for the same reason, since one 100 pCi/L basement would drag an average for a whole ZIP and a median it cannot.
A ZIP code is not a house. The spread between two homes on the same street is routinely wider than the spread between two ZIP codes. A low median where you live is not evidence your own house is low, and a high one is not evidence it is high. It tells you how common a problem is nearby, and nothing whatsoever about your foundation.
482 of the 1,118 ZIP codes here have fewer than 30 tests. They appear in grey. We would rather show you an honest blank than a confident colour built on nine houses.
The extremes in this data are real, and they are rare. Sixty six of the 498,825 readings are at or above 100 pCi/L and twelve are at or above 200, the highest being 1,403. They turn up in different ZIP codes, different counties and on different equipment, so they are not one broken meter. They are also about one home in seven thousand. The reason to test is the ordinary result, not that one.
The highest ZIP codes in Illinois
Ranked by median reading, and restricted to ZIP codes with at least 30 tests. The sample size sits beside every row because it is the thing that decides whether a row means anything.
| ZIP | Tests | Median pCi/L | At or above 4.0 | Highest single |
|---|---|---|---|---|
| 61062 | 32 | 11.6 | 65.6% | 103.5 |
| 61413 | 41 | 8.9 | 73.2% | 36.7 |
| 61840 | 35 | 8.5 | 68.6% | 21.6 |
| 61085 | 91 | 8.2 | 76.9% | 39.2 |
| 61537 | 78 | 8.2 | 70.5% | 37.6 |
| 61231 | 172 | 7.95 | 66.3% | 43.5 |
| 61273 | 179 | 7.9 | 75.4% | 49.1 |
| 61327 | 42 | 7.9 | 76.2% | 136.8 |
| 61559 | 242 | 7.65 | 64.9% | 49.1 |
| 61001 | 166 | 7.6 | 69.9% | 779 |
| 61012 | 35 | 7.6 | 68.6% | 22.6 |
| 61238 | 87 | 7.6 | 74.7% | 37.4 |
| 61019 | 301 | 7.5 | 67.8% | 67.3 |
| 61570 | 60 | 7.4 | 63.3% | 48.7 |
| 61747 | 39 | 7.4 | 61.5% | 17.8 |
The most-tested ZIP codes
Where Illinois has the most data. These are the rows to trust most, and several of them sit close to or above the action level on a sample of thousands of homes.
| ZIP | Tests | Median pCi/L | At or above 4.0 |
|---|---|---|---|
| 60564 | 10,025 | 2.5 | 29.2% |
| 60540 | 8,614 | 2.9 | 38.8% |
| 60565 | 7,720 | 2.7 | 36.9% |
| 60010 | 7,510 | 2.6 | 30.5% |
| 60134 | 6,651 | 2.7 | 33.6% |
| 61704 | 6,599 | 3.2 | 41.4% |
| 61761 | 6,497 | 3.6 | 46.7% |
| 60137 | 6,072 | 2.7 | 35.8% |
| 60047 | 5,754 | 2.7 | 31.5% |
| 62704 | 5,410 | 3.7 | 45.6% |
What the numbers mean
The EPA acts at 4.0 pCi/L and recommends you consider acting between 2.0 and 4.0. The World Health Organization sets its reference level lower, at 100 Bq/m³, which is about 2.7 pCi/L. Every one of these is an action level rather than a safety guarantee. There is no reading below which radon is known to be harmless, which is why the advice is to test and then decide, rather than to look up your ZIP code and stop.
On this data, 35.8% of Illinois homes tested are at or above the EPA action level. That is roughly one in three, in a state where the law already puts a radon pamphlet in front of every buyer.
If your reading is high
A high result is a fixable problem, not a disaster. Mitigation is a pipe and a fan that vents soil gas above the roofline, and it usually takes a day. The distinction that matters when you start calling is that measuring and mitigating are separate certifications: plenty of companies can test your house and cannot fix it. Our Illinois directory lists every certified company in the state and splits them by which of the two they are actually certified to do.
Source. Radon measurement data published by the Illinois Emergency Management Agency, Office of Homeland Security, covering 2003-2019. Aggregated here to ZIP code level. Individual addresses are recorded in the state's file and are deliberately not reproduced on this site. Boundaries are US Census Bureau 2020 cartographic ZCTAs, public domain. Invalid tests flagged as such by the state are excluded, and readings recorded below zero are treated as zero rather than discarded.
This page is an educational summary of public records. It is not a health assessment of any individual property, and no reading here should be used to price a house or to decide against testing one.