Illiopolis Weather Forecast

    • 69
    • 84

    Becoming Sunny

    • 68
    • 95

    Chance Thunderstorms

    • 71
    • 91

    Chance Rain Showers

    • 67
    • 90

    Slight Chance Thunderstorms

    • 66
    • 86

    Slight Chance Thunderstorms

    • 64
    • 87

    Chance Rain Showers

Today 14 Sep Sangamon

Mostly sunny. Highs in the mid 80s. Southeast Winds 10 to 15 Mph.

Tonight 14 Sep Sangamon

Mostly clear. Not as cool with Lows around 70. South Winds 10 to 15 Mph with Gusts up to 25 Mph.

Graph Plots Open in Graphs

  • Temperature Forecast NOAA

  • Temperature Real-Time

Illiopolis Temperature Statistics

September Temperature

Decatur Airport (19.3 miles)

  • Lowest 7 September, 2026

    55.7 °F

  • Average September

    78.8 °F

  • Highest 4 September, 2026

    98.7 °F

Climate (2021–2026)

Decatur Airport (19.3 miles)

Take a look at our website widgetsAvailable free! Find Out More

  • Average Low 2021–2026

    45.4 °F

  • Average 2021–2026

    55.6 °F

  • Average High 2021–2026

    65.6 °F
Get WillyWeather+ to remove ads