Grundy County Climate
Grundy County, Illinois
Avg Annual Temp
51.0°F
Annual Precip
38.0"
Annual Snowfall
21.5"
Extreme Heat Days
20.1
days >= 90°F/yr
Monthly Temperature
Precipitation Calendar
Seasonal Overview
National Comparison
Climate Profile
About Grundy County Weather
Cooler Northern Continental Climate
Grundy County averages 51.0°F annually, placing it below the national median. This region is known for colder winters and brisk autumns.
Below the Illinois Average
The annual average of 51.0°F is nearly two degrees cooler than the state average of 52.8°F. This reflects the county's northern position and exposure to Great Lakes influences.
Low Precipitation for the Region
Grundy receives 38.0 inches of annual precipitation, which is lower than the 41.7-inch state average. It is one of the drier counties in the northern half of Illinois.
Snowy Winters and Warm Summers
Winters are significant with 21.5 inches of annual snowfall and a 23.9°F January average. Summers still bring 20 days of extreme heat where temperatures reach or exceed 90°F.
Invest in Winter Durability
The 21.5-inch snowfall average requires heavy-duty winter gear and effective home insulation. Residents should also prepare for the 20 annual heat days with reliable air conditioning.
Frequently Asked Questions
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Data source: NOAA National Centers for Environmental Information (NCEI), U.S. Climate Normals 1991-2020.
Climate normals are 30-year averages of weather variables computed from 1991 to 2020. Station data is aggregated to county level using spatial averaging. Data is informational only — not a substitute for official National Weather Service forecasts or emergency weather warnings.