Radon levels in St. Clair County, Illinois
ModerateEPA Zone 2Predicted long-term basement average of 2.2 pCi/L (model estimate) across 25 ZIP codes - about 1.2× the US average of 1.8, about 1.2× the Illinois average of 1.9. Ranked #64 of 102 Illinois counties.
Test St. Clair County, IL - the EPA says "consider fixing" in this range
The predicted basement average here is 2.2 pCi/L, in the 2-4 pCi/L band where the EPA recommends considering mitigation. Plenty of individual homes in a moderate area test above 4. Start with a short-term test; if it comes back at 2 or higher, follow up with a long-term test or a continuous monitor.
Already tested at 4 pCi/L or higher? Find a certified mitigation professional (EPA). A mitigation system typically runs $800-$2,500 installed.
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Predicted (model estimate). The pCi/L figures on this page are long-term area averages from a peer-reviewed national model built on millions of real radon tests (2001-2021). They describe the typical home in this area - not your home, which can be several times higher or lower. The EPA radon zone is a separate, 1993 county-level classification. How the numbers work.
2.2 ± 0.06
pCi/L predicted basement mean (model SD)
1.1 ± 0.07
pCi/L predicted upstairs (above-ground) mean
1.4-2.9
range of ZIP-level basement predictions in the county
What this means for St. Clair
The typical St. Clair County home is predicted in the 2-4 pCi/L band. The EPA's guidance for this range is to consider fixing, because there is no known safe level and roughly one home in several in a moderate area will test above 4.
The 1993 EPA zone (2) and the 2001-2021 model agree for St. Clair. County figures weight each ZIP by its 2010 Census population, so they describe where people live rather than empty land.
Comparable Illinois counties: Union County (2.2), Randolph County (2.2), Kane County (2.2), Washington County (2.3). The state's highest is Knox County at 4.0 pCi/L.
ZIP codes in St. Clair County
Predicted basement and upstairs means by ZIP (model estimate). ZIPs whose land is mostly in this county.
| ZIP | Basement | Upstairs | Grade |
|---|---|---|---|
| 62269 | 2.3 ± 0.07 | 1.2 | Moderate |
| 62226 | 2.5 ± 0.06 | 1.1 | Moderate |
| 62221 | 2.6 ± 0.06 | 1.5 | Moderate |
| 62220 | 2.6 ± 0.05 | 1.1 | Moderate |
| 62223 | 2.2 ± 0.04 | 1.1 | Moderate |
| 62208 | 2.4 ± 0.05 | 1.3 | Moderate |
| 62206 | 1.6 ± 0.08 | 1.0 | Low |
| 62205 | 1.5 ± 0.08 | 0.9 | Low |
| 62258 | 2.9 ± 0.09 | 1.3 | Moderate |
| 62207 | 1.7 ± 0.07 | 0.8 | Low |
| 62203 | 1.4 ± 0.11 | 0.8 | Low |
| 62204 | 1.6 ± 0.07 | 0.8 | Low |
| 62201 | 1.5 ± 0.07 | 0.8 | Low |
| 62260 | 2.3 ± 0.06 | 1.3 | Moderate |
| 62232 | 2.0 ± 0.05 | 1.2 | Low |
| 62254 | 2.4 ± 0.05 | 1.4 | Moderate |
| 62243 | 2.3 ± 0.05 | 1.2 | Moderate |
| 62225 | 2.1 ± 0.06 | 1.2 | Moderate |
| 62239 | 2.2 ± 0.05 | 1.4 | Moderate |
| 62285 | 2.2 ± 0.05 | 1.1 | Moderate |
| 62264 | 2.2 ± 0.06 | 1.0 | Moderate |
| 62257 | 2.1 ± 0.06 | 1.2 | Moderate |
| 62240 | 1.9 ± 0.06 | 0.9 | Low |
| 62255 | 2.0 ± 0.06 | 1.1 | Moderate |
| 62059 | 1.7 ± 0.07 | 0.9 | Low |
If your test comes back at 4 pCi/L or higher
Mitigation is a routine job: a fan-driven pipe that vents soil gas from under the slab to above the roofline, typically $800-$2,500 installed (typical range; local quotes vary). Use certified professionals: EPA find-a-professional. Read the full mitigation guide.
St. Clair County radon questions
- Is radon high in St. Clair County, Illinois?
- Moderate. The model predicts a long-term basement average of 2.2 pCi/L in St. Clair County (about 1.2× the US average of 1.8 and about 1.2× the Illinois average of 1.9). That is in the 2-4 pCi/L range where the EPA recommends considering mitigation. Ranked 64 of 102 Illinois counties.
- Should I test for radon in St. Clair County?
- Yes, soon. With a predicted average of 2.2 pCi/L, many homes in St. Clair County will test above the 4 pCi/L action level. Use a short-term kit first; if it reads 2 or higher, confirm with a long-term test or continuous monitor before deciding on mitigation.
- What does EPA Radon Zone 2 mean for St. Clair County?
- Zone 2 - moderate potential (2-4 pCi/L). The zone map dates from 1993 and classifies whole counties. The 2001-2021 model agrees with the zone here. Neither replaces a test of your own home.
- How much does radon mitigation cost in St. Clair County?
- A standard active sub-slab depressurization system typically runs $800-$2,500 installed nationally; Illinois quotes vary with foundation type (slab, crawlspace, basement), home size and local labor. Get two or three bids from certified mitigators listed by your state radon program or the EPA's find-a-professional page.
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