Illiopolis Weather Forecast

    • 17
    • 26

    Increasing Clouds

    • 35
    • 42

    Chance Rain

    • 21
    • 41

    Chance Snow

    • 20
    • 31

    Chance Snow

    • 7
    • 28

    Mostly Cloudy

    • 5
    • 15

    Mostly Cloudy

    • 11
    • 20

    Mostly Cloudy

Today 8 Dec Sangamon

Mostly sunny. Near steady temperature in the lower 20s. South Winds around 5 Mph.

Tonight 8 Dec Sangamon

Partly cloudy this Evening, then becoming mostly cloudy. Lows around 18. Temperature rising into the upper 20s after midnight. South Winds 10 to 15 Mph with Gusts up to 25 Mph.

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  • Temperature Forecast NOAA

  • Temperature Real-Time

Illiopolis Temperature Statistics

December Temperature

Decatur Airport (19.3 miles)

  • Lowest 4 December, 2025

    1 °F

  • Average December

    21.9 °F

  • Highest 6 December, 2025

    35.1 °F

Climate (2020–Present)

Decatur Airport (19.3 miles)

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  • Average Low 2020–2025

    45.3 °F

  • Average 2020–2025

    55.3 °F

  • Average High 2020–2025

    65.2 °F
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