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.
Tonight
55°F
Rain
Rain before 3am, then a slight chance of drizzle. Mostly cloudy, with a low around 55. Southwest wind 9 to 15 mph, with gusts as high as 26 mph. Chance of precipitation is 90%.
7-day forecast for O'Fallon
| When | Temp | Forecast | Wind | Precip |
|---|---|---|---|---|
| Tonight | 55°F | Rain | 9 to 15 mph SW | 85% |
| Wednesday | 63°F | Slight Chance Drizzle then Mostly Cloudy | 7 to 14 mph W | 12% |
| Wednesday Night | 45°F | Partly Cloudy | 6 mph W | 0% |
| Thursday | 65°F | Sunny | 6 to 12 mph W | 1% |
| Thursday Night | 46°F | Mostly Cloudy | 5 mph NW | 7% |
| Friday | 58°F | Partly Sunny | 5 to 12 mph NW | 7% |
| Friday Night | 40°F | Partly Cloudy | 2 to 7 mph N | 1% |
| Saturday | 56°F | Partly Sunny | 5 mph NW | 0% |
| Saturday Night | 37°F | Partly Cloudy | 1 mph NW | 0% |
| Sunday | 62°F | Sunny | 1 to 7 mph W | 8% |
| Sunday Night | 37°F | Mostly Clear | 5 mph W | 5% |
| Monday | 66°F | Sunny | 2 to 8 mph SW | 2% |
| Monday Night | 42°F | Mostly Clear | 3 mph SW | 1% |
| Tuesday | 69°F | Sunny | 6 mph W | 0% |
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.