Decatur Illinois Climate Data

Monthly Average Climate Data for Decatur Illinois

Switch Data to Celsius/Metric Units
MonthAvg. LowAvg. HighAvg. Precip
January18.9 °F35.0 °F2.33 in.
February21.6 °F39.9 °F2.02 in.
March30.8 °F51.0 °F2.72 in.
April41.9 °F64.2 °F4.19 in.
May53.4 °F74.2 °F4.64 in.
June61.9 °F83.2 °F4.72 in.
July65.0 °F86.0 °F3.64 in.
August63.2 °F84.4 °F3.29 in.
September54.9 °F79.4 °F3.13 in.
October43.1 °F66.7 °F3.3 in.
November32.4 °F51.8 °F3.12 in.
December24.7 °F39.8 °F2.42 in.
Annual42.7 °F63 °F39.52 in.

Climate Data for Decatur Illinois

Average First Frost DateOct. 11 - Oct. 20
Average Last Frost DateMay 1 - May 10
Average Days With Frost100-125 Days
Plant Hardiness Zone - 2023Zone 6a : -10°F to -5°F
Plant Hardiness Zone - 2012Zone 5b : -15°F to -10°F
Current Drought ConditionsNormal
Köppen Climate ClassificationDfa - Humid Continental Hot Summers With Year Around Precipitation