OFallon is a city of approximately 29,000 people in Illinois, United States. Located in the Central Time Zone at 38.6°N latitude.
In 2025, OFallon recorded an average annual temperature of 56°F — about 1.3°F below the 30-year normal of 58°F. The hottest day reached 96°F in July; the coldest was -0°F in February. Total precipitation was 44 inches (near normal). Snowfall totaled 6 inches, below the 11-inch average. The wettest month was April.
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