O'Fallon, IL Weather & Growing Conditions
Local forecast, frost dates, hardiness zone and planting guidance for O'Fallon, a city in St. Clair County, Illinois.
Overnight
56°F
Slight Chance Drizzle
A slight chance of drizzle. Mostly cloudy, with a low around 56. Southwest wind around 8 mph.
7-day forecast for O'Fallon
| When | Temp | Forecast | Wind | Precip |
|---|---|---|---|---|
| Overnight | 56°F | Slight Chance Drizzle | 8 mph SW | 14% |
| Wednesday | 60°F | Slight Chance Drizzle then Mostly Cloudy | 8 to 14 mph W | 12% |
| Wednesday Night | 45°F | Partly Cloudy | 6 mph W | 0% |
| Thursday | 65°F | Sunny | 6 to 12 mph W | 0% |
| Thursday Night | 47°F | Partly Cloudy | 5 mph NW | 2% |
| Friday | 57°F | Partly Sunny | 6 to 13 mph N | 1% |
| Friday Night | 37°F | Partly Cloudy | 2 to 8 mph N | 0% |
| Saturday | 55°F | Mostly Sunny | 5 mph N | 0% |
| Saturday Night | 35°F | Partly Cloudy | 2 mph NW | 0% |
| Sunday | 59°F | Sunny | 2 to 7 mph NW | 1% |
| Sunday Night | 36°F | Clear | 2 mph W | 0% |
| Monday | 66°F | Sunny | 1 to 6 mph SW | 0% |
| Monday Night | 42°F | Clear | 2 mph SW | 0% |
| Tuesday | 69°F | Sunny | 5 mph W | 1% |
Forecast source: National Weather Service (api.weather.gov) for O'Fallon (38.600, -89.915). Updated through the day.
Growing snapshot for O'Fallon
Last spring frost
Apr 12
First fall frost
Oct 20
Growing season
189 days
Hardiness zone
7a
More local growing data for O'Fallon: nearby ZIP 62269 weather · frost dates · planting calendar · Illinois frost dates
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Climate data from the nearest NOAA station, Belleville Siu Rsch, Il (6.7 mi from O'Fallon). Frost dates are 1991–2020 averages, not a forecast. Page updated Nov 4, 2026.