Is radon high in O'Fallon, Missouri?

Low. Averaging the model's ZIP-code predictions across O'Fallon (weighted by how much of the city each ZIP covers) gives a long-term basement mean of 1.9 pCi/L - close to the US average of 1.8 and close to the Missouri average of 2.2. That is below the EPA's 2 pCi/L "consider fixing" threshold, though individual homes still vary. O'Fallon ranks 11 of 15 Missouri cities on this site.

Which O'Fallon ZIP codes have the highest radon?

Predictions for the 6 modeled ZIP codes in O'Fallon range from 1.8 to 2.4 pCi/L in the basement. 0% of them are predicted at or above 4 pCi/L and 67% at or above 2. The city is fairly uniform, so the city-wide number is a reasonable guide for any neighborhood.

Should I test for radon in O'Fallon?

Yes, once. The EPA recommends testing every home regardless of area. A short-term kit costs little and settles the question for your house; O'Fallon's low predicted average describes the typical home, not yours.

What does EPA Radon Zone 2 mean for O'Fallon?

O'Fallon sits mainly in St. Charles County, which the EPA classifies as Zone 2 - moderate potential (2-4 pCi/L). The zone map dates from 1993 and covers whole counties. The newer model's city average of 1.9 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.

Radon levels in O'Fallon, Missouri

LowEPA Zone 2

Predicted long-term basement average of 1.9 pCi/L (model estimate) across the 6 modeled ZIP codes in O'Fallon - close to the US average of 1.8, close to the Missouri average of 2.2. Ranked #11 of 15 Missouri cities on this site. Most of the city lies in St. Charles County.

Test O'Fallon, MO once anyway - radon varies house to house

The predicted basement average here is 1.9 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.

1.9 ± 0.07

pCi/L predicted basement mean (model SD)

0.9 ± 0.07

pCi/L predicted upstairs (above-ground) mean

1.8-2.4

range of ZIP-level basement predictions in the city

of O'Fallon ZIPs predicted ≥ 4 pCi/L (67% ≥ 2)

What this means for O'Fallon

The typical O'Fallon home is predicted below 2 pCi/L, the lowest band. That describes the average house; the ZIP-level predictions inside the city still span 1.8 to 2.4 pCi/L.

The city figure is not a separate estimate: it is the mean of the model's ZIP-code predictions, weighted by the share of the city's land in each ZIP (Census 2020 ZCTA-to-place relationship file). Note that the EPA classifies St. Charles County as Zone 2 while the newer model predicts 1.9 pCi/L for O'Fallon; where they disagree, we grade on the model but show both.

Comparable Missouri cities: Columbia (1.9), Chesterfield (1.9), Wentzville (2.0), St. Peters (2.0).

ZIP codes in O'Fallon

ZIPs that overlap the city, largest share of its land first. Predicted basement and upstairs means are model estimates; ZIPs the model does not cover show a dash.

ZIP	Share of city	Basement	Upstairs	Grade
63366	54%	2.0 ± 0.07	0.8	Moderate
63368	30%	1.7 ± 0.08	1.0	Low
63376	7%	2.1 ± 0.07	1.2	Moderate
63367	5%	2.4 ± 0.08	1.2	Moderate
63304	2%	1.8 ± 0.07	1.4	Low
63385	2%	2.0 ± 0.07	1.3	Moderate

Testing help in Missouri

Missouri's radon program page is at health.mo.gov and, when we checked it, offered free radon test kits for Missouri residents. EPA state radon contacts page. If a test comes back at 4 pCi/L or higher, mitigation typically costs $800-$2,500 installed; use EPA find-a-professional and read the mitigation guide.

O'Fallon radon questions

Is radon high in O'Fallon, Missouri?: Low. Averaging the model's ZIP-code predictions across O'Fallon (weighted by how much of the city each ZIP covers) gives a long-term basement mean of 1.9 pCi/L - close to the US average of 1.8 and close to the Missouri average of 2.2. That is below the EPA's 2 pCi/L "consider fixing" threshold, though individual homes still vary. O'Fallon ranks 11 of 15 Missouri cities on this site.
Which O'Fallon ZIP codes have the highest radon?: Predictions for the 6 modeled ZIP codes in O'Fallon range from 1.8 to 2.4 pCi/L in the basement. 0% of them are predicted at or above 4 pCi/L and 67% at or above 2. The city is fairly uniform, so the city-wide number is a reasonable guide for any neighborhood.
Should I test for radon in O'Fallon?: Yes, once. The EPA recommends testing every home regardless of area. A short-term kit costs little and settles the question for your house; O'Fallon's low predicted average describes the typical home, not yours.
What does EPA Radon Zone 2 mean for O'Fallon?: O'Fallon sits mainly in St. Charles County, which the EPA classifies as Zone 2 - moderate potential (2-4 pCi/L). The zone map dates from 1993 and covers whole counties. The newer model's city average of 1.9 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.

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