Illiopolis Weather Forecast

    • 57
    • 68

    Chance Rain Showers

    • 52
    • 69

    Partly Sunny

    • 52
    • 72

    Partly Sunny

    • 54
    • 73

    Mostly Cloudy

    • 54
    • 75

    Mostly Cloudy

    • 56
    • 77

    Mostly Cloudy

Today 21 Sep Sangamon

Cloudy. A chance of Showers with a slight chance of Thunderstorms in the morning. Much cooler with Highs around 70. Northeast Winds around 10 Mph. Chance of rain 40 percent.

Tonight 21 Sep Sangamon

Mostly cloudy. Lows in the upper 50s. Northeast Winds 5 to 10 Mph.

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Illiopolis Temperature Statistics

September Temperature

Decatur Airport (19.3 miles)

  • Lowest 14 September, 2026

    54.6 °F

  • Average September

    78.2 °F

  • Highest 15 September, 2026

    99.6 °F

Climate (2021–2026)

Decatur Airport (19.3 miles)

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  • Average Low 2021–2026

    45.4 °F

  • Average 2021–2026

    55.6 °F

  • Average High 2021–2026

    65.7 °F
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