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O'Fallon, IL
Full City Profile · Illinois · St. Clair County County
4.0
/5.0
A
Great
32,139
Population
2,033/sq mi density
$102,793
Median Income
$51,826 per capita
$274,100
Home Value
$306,969 Zillow
$1,312
Median Rent
27.2% income on rent
58°F
Avg Temperature
293 sunny days/yr
179
Violent Crime/100K
1,425 property/100K
A
Overall
4.0 / 5.0
Strong
A+
Economy
5.0 / 5.0
$102,793 median income, 2.1% unemployment
A+
Affordability
5.0 / 5.0
$274,100 home value, $1,312/mo rent
F
Safety
1.0 / 5.0
179 violent crimes/100K
A+
Education
5.0 / 5.0
51.3% bachelor's degree or higher
O'Fallon enjoys a temperate climate with an average annual temperature of 58°F (14°C). Winters average 34°F in January while summers reach 79°F in July. The area gets 293 sunny days per year. Annual precipitation totals 43.4 inches. The area receives 11.2 inches of snow annually. Air quality is rated Good with a median AQI of 43.
Temperature
34°F Jan (1°C)
79°F Jul (26°C)
| Annual Average | 57.7°F |
| 7% above US avg | |
| January Average | 34°F (1°C) |
| July Average | 79°F (26°C) |
| Sunny Days | 293 days/yr |
Geography
| Elevation | 535 ft (163 m) |
| Area | 14.5 sq mi (37.5 km²) |
| Population Density | 2,033/sq mi |
| Coordinates | 38.6000°N, 89.9154°W |
| Timezone | America/Chicago |
| County | St. Clair County County |
| Nearest Airport | St Louis Regional (ALN) 21 miles away |
Precipitation & Snow
Air Quality
| AQI Median | 43.0 |
| Rating | Good |
Air Pollutants (EPA 2023)
| Ozone (O₃) | 0.0482 ppm |
| NO₂ (Nitrogen Dioxide) | 14.2 ppb |
| SO₂ (Sulfur Dioxide) | 1.12 ppb |
| PM2.5 (Fine Particles) | 10.5 μg/m³ |
Natural Hazard Risk
| Overall Risk | Relatively High |
| Risk Score | 94.9 / 100 |
| Social Vulnerability | 37.9 / 100 |
| Community Resilience | 74.9 / 100 |
Hazard Breakdown
| Tornado | Relatively High |
| Hurricane | Very Low |
| Earthquake | Relatively Moderate |
| Wildfire | Very Low |
| Flood | Relatively High |
| Hail | Relatively High |
| Strong Wind | Relatively Moderate |
| Heat Wave | Relatively High |
| Winter Weather | Relatively High |
| Lightning | Relatively High |
| Ice Storm | Relatively High |
| Drought | Relatively Low |
| Cold Wave | Relatively High |
| Landslide | Relatively Low |
Source: FEMA National Risk Index v1.20 (Dec 2025)
Monthly Weather
| Month | Avg Temperature | Precipitation | Summary |
|---|---|---|---|
| January | 34°F (1°C) | 2.1 in | Coldest, Driest |
| February | 34°F (1°C) | 2.3 in | |
| March | 44°F (7°C) | 3.4 in | |
| April | 55°F (13°C) | 3.7 in | |
| May | 65°F (18°C) | 4.1 in | Wettest |
| June | 74°F (23°C) | 3.7 in | |
| July | 79°F (26°C) | 3.7 in | Warmest |
| August | 76°F (24°C) | 3.2 in | |
| September | 69°F (20°C) | 3.3 in | |
| October | 57°F (14°C) | 2.7 in | |
| November | 45°F (7°C) | 3.1 in | |
| December | 34°F (1°C) | 2.9 in |
O'Fallon has a seasonal temperature swing of 45°F / from 34°F in January to 79°F in July. Total annual precipitation is 38.1 inches, with May being the wettest month (4.1") and January the driest (2.1").