O'Fallon, IL Weather & Growing Conditions
Tonight
73°F
Partly Cloudy
Partly cloudy, with a low around 73. Southeast wind 2 to 6 mph.
7-day forecast
| 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). Updated through the day.
Growing snapshot for O'Fallon, IL
Last spring frost
Apr 12
First fall frost
Oct 20
Growing season
189 days
Hardiness zone
7a
Explore more for O'Fallon, IL: full frost dates · planting calendar · Illinois frost dates
Climate data from the nearest NOAA station, Belleville Siu Rsch, Il (6.7 mi). Frost dates are 1991–2020 averages, not a forecast. Page updated Sep 19, 2026.