Radon levels in St. Louis County, Missouri
LowEPA Zone 2Predicted long-term basement average of 1.8 pCi/L (model estimate) across 42 ZIP codes - close to the US average of 1.8, about 15% below the Missouri average of 2.2. Ranked #107 of 115 Missouri counties.
Test St. Louis County, MO once anyway - radon varies house to house
The predicted basement average here is 1.8 pCi/L, below the EPA's 2 pCi/L "consider fixing" threshold. That's good news for the area - but the EPA still recommends every home be tested, because foundation cracks, soil pockets and ventilation make one house very different from its neighbor. One inexpensive kit settles it.
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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.
1.8 ± 0.08
pCi/L predicted basement mean (model SD)
1.1 ± 0.08
pCi/L predicted upstairs (above-ground) mean
1.1-2.5
range of ZIP-level basement predictions in the county
What this means for St. Louis
The typical St. Louis County home is predicted below 2 pCi/L, the lowest band. That is the best case an area can show - but it describes the average house, and the ZIP-level predictions within the county still span 1.1 to 2.5 pCi/L.
Note that the EPA classifies St. Louis County as Zone 2 while the newer model predicts 1.8 pCi/L. The zone map predates two decades of test data; where they disagree, we grade on the model but show both. County figures weight each ZIP by its 2010 Census population, so they describe where people live rather than empty land.
Comparable Missouri counties: Camden County (1.8), Butler County (1.8), Ripley County (1.9), Wayne County (1.9). The state's highest is Atchison County at 4.4 pCi/L.
ZIP codes in St. Louis County
Predicted basement and upstairs means by ZIP (model estimate). ZIPs whose land is mostly in this county.
| ZIP | Basement | Upstairs | Grade |
|---|---|---|---|
| 63021 | 2.0 ± 0.07 | 1.4 | Moderate |
| 63129 | 2.5 ± 0.09 | 1.4 | Moderate |
| 63123 | 1.9 ± 0.06 | 1.1 | Low |
| 63136 | 1.4 ± 0.14 | 0.4 | Low |
| 63031 | 1.8 ± 0.06 | 1.2 | Low |
| 63033 | 1.9 ± 0.06 | 1.1 | Low |
| 63017 | 1.9 ± 0.06 | 1.3 | Low |
| 63122 | 1.8 ± 0.06 | 1.2 | Low |
| 63011 | 1.7 ± 0.08 | 1.3 | Low |
| 63114 | 1.5 ± 0.08 | 0.9 | Low |
| 63119 | 1.9 ± 0.06 | 1.3 | Low |
| 63125 | 2.0 ± 0.09 | 1.3 | Low |
| 63130 | 1.5 ± 0.09 | 0.9 | Low |
| 63128 | 2.3 ± 0.08 | 1.3 | Moderate |
| 63146 | 2.1 ± 0.07 | 1.2 | Moderate |
| 63121 | 1.4 ± 0.10 | 0.8 | Low |
| 63043 | 1.8 ± 0.09 | 1.3 | Low |
| 63135 | 1.6 ± 0.07 | 0.9 | Low |
| 63137 | 1.1 ± 0.17 | 0.8 | Low |
| 63141 | 1.9 ± 0.07 | 1.2 | Low |
| 63138 | 1.8 ± 0.05 | 1.2 | Low |
| 63042 | 1.9 ± 0.06 | 1.1 | Low |
| 63034 | 2.0 ± 0.06 | 1.2 | Moderate |
| 63005 | 1.9 ± 0.08 | 1.1 | Low |
| 63105 | 1.7 ± 0.09 | 1.0 | Low |
| 63131 | 1.9 ± 0.09 | 1.3 | Low |
| 63074 | 1.6 ± 0.08 | 0.8 | Low |
| 63126 | 1.9 ± 0.07 | 1.2 | Low |
| 63132 | 1.8 ± 0.06 | 1.1 | Low |
| 63025 | 2.3 ± 0.07 | 1.3 | Moderate |
| 63134 | 1.3 ± 0.10 | 0.6 | Low |
| 63044 | 2.2 ± 0.06 | 1.2 | Moderate |
| 63124 | 1.9 ± 0.05 | 1.2 | Low |
| 63143 | 1.6 ± 0.06 | 0.9 | Low |
| 63117 | 1.7 ± 0.06 | 0.9 | Low |
| 63144 | 1.8 ± 0.07 | 1.1 | Low |
| 63040 | 1.7 ± 0.06 | 1.2 | Low |
| 63088 | 1.9 ± 0.06 | 1.3 | Low |
| 63133 | 1.5 ± 0.12 | 0.6 | Low |
| 63038 | 2.1 ± 0.09 | 1.3 | Moderate |
| 63127 | 2.2 ± 0.07 | 1.4 | Moderate |
| 63140 | 1.7 ± 0.07 | 0.8 | 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. Louis County radon questions
- Is radon high in St. Louis County, Missouri?
- Low. The model predicts a long-term basement average of 1.8 pCi/L in St. Louis County (close to the US average of 1.8 and about 15% below the Missouri average of 2.2). That is below the EPA's 2 pCi/L "consider fixing" threshold, though individual homes still vary. Ranked 107 of 115 Missouri counties.
- Should I test for radon in St. Louis County?
- Yes, once. The EPA recommends testing every home regardless of area, and the model's ZIP-level predictions in St. Louis County already range from 1.1 to 2.5 pCi/L. A short-term kit costs little and settles the question for your house.
- What does EPA Radon Zone 2 mean for St. Louis County?
- Zone 2 - moderate potential (2-4 pCi/L). The zone map dates from 1993 and classifies whole counties. The newer model's predicted average of 1.8 pCi/L does not line up with Zone 2, which is common - the EPA itself says high-radon homes exist in every zone. Neither replaces a test of your own home.
- How much does radon mitigation cost in St. Louis County?
- A standard active sub-slab depressurization system typically runs $800-$2,500 installed nationally; Missouri 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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