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
73°F
Partly Cloudy
Partly cloudy, with a low around 73. Southeast wind 2 to 6 mph.
7-day forecast for O'Fallon
| When | Temp | Forecast | Wind | Precip |
|---|---|---|---|---|
| Tonight | 73°F | Partly Cloudy | 2 to 6 mph SE | 12% |
| Saturday | 97°F | Mostly Sunny | 3 to 8 mph SW | 6% |
| Saturday Night | 73°F | Partly Cloudy | 5 mph S | 1% |
| Sunday | 94°F | Mostly Sunny then Slight Chance Showers And Thunderstorms | 3 to 8 mph W | 18% |
| Sunday Night | 68°F | Slight Chance Showers And Thunderstorms then Showers And Thunderstorms Likely | 8 mph N | 56% |
| Monday | 81°F | Rain Showers Likely | 7 to 12 mph N | 67% |
| Monday Night | 61°F | Showers And Thunderstorms Likely | 7 to 13 mph N | 67% |
| Tuesday | 72°F | Chance Rain Showers then Mostly Cloudy | 13 mph N | 28% |
| Tuesday Night | 55°F | Mostly Cloudy | 6 to 13 mph N | 6% |
| Wednesday | 74°F | Mostly Sunny | 7 to 10 mph N | 3% |
| Wednesday Night | 56°F | Partly Cloudy | 3 to 9 mph N | 2% |
| Thursday | 76°F | Mostly Sunny | 3 to 9 mph N | 2% |
| Thursday Night | 58°F | Partly Cloudy | 3 to 8 mph N | 2% |
| Friday | 76°F | Mostly Sunny | 5 to 8 mph N | 5% |
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 Sep 19, 2026.