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.

Today

87°F

Sunny

Sunny, with a high near 87. Southeast wind 2 to 6 mph.

7-day forecast for O'Fallon

When	Temp	Forecast	Wind	Precip
Today	87°F	Sunny	2 to 6 mph SE	0%
Tonight	67°F	Mostly Clear	2 to 6 mph SE	0%
Wednesday	90°F	Sunny	2 to 6 mph S	6%
Wednesday Night	72°F	Slight Chance Showers And Thunderstorms	7 mph S	63%
Thursday	87°F	Showers And Thunderstorms Likely	7 mph S	72%
Thursday Night	70°F	Chance Showers And Thunderstorms	5 mph SE	45%
Friday	87°F	Chance Showers And Thunderstorms	3 mph SW	45%
Friday Night	70°F	Chance Showers And Thunderstorms	3 mph SW	36%
Saturday	89°F	Chance Showers And Thunderstorms	5 mph S	36%
Saturday Night	72°F	Partly Cloudy	7 mph S	9%
Sunday	92°F	Sunny	5 to 9 mph S	7%
Sunday Night	74°F	Mostly Clear	6 to 9 mph S	5%
Monday	93°F	Mostly Sunny	6 to 9 mph SW	5%
Monday Night	75°F	Slight Chance Showers And Thunderstorms	9 mph S	15%

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

More local growing data for O'Fallon: nearby ZIP 62269 weather · frost dates · planting calendar · Illinois frost dates

Nearby towns & communities

Belleville Brooklyn Cahokia Heights Caseyville Darmstadt Dupo East St. Louis Fairmont City Fairview Heights Fayetteville Floraville Freeburg Lebanon Lenzburg Marissa Mascoutah Millstadt New Athens Paderborn Rentchler Sauget Scott AFB Shiloh Smithton St. Libory Summerfield Swansea Washington Park

All Illinois locations ›

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 Aug 4, 2026.