Hamilton County Climate
Hamilton County, Illinois
Avg Annual Temp
55.4°F
Annual Precip
47.1"
Annual Snowfall
13.3"
Extreme Heat Days
42.6
days >= 90°F/yr
Monthly Temperature
Precipitation Calendar
Seasonal Overview
National Comparison
Climate Profile
About Hamilton County Weather
Warm and Wet Southern Climate
Hamilton County's 55.4°F annual average temperature is warmer than the national median. Its climate is characterized by significant rainfall and prolonged summer heat.
One of Illinois' Warmest Counties
Averaging 55.4°F, Hamilton is nearly three degrees warmer than the Illinois state average of 52.8°F. It is consistently among the top tier for heat in the state.
Maximum Precipitation in the Region
With 47.1 inches of annual precipitation, Hamilton is much wetter than the state average of 41.7 inches. It shares this humid, high-rainfall profile with neighbor Gallatin County.
Intense Heat and Minimal Snow
The county endures 43 extreme heat days per year where temperatures exceed 90°F. In contrast, it receives only 13.3 inches of snow, making for relatively easy winters.
Beat the Southern Illinois Heat
With over 40 days of extreme heat, robust air conditioning is a non-negotiable for safety and comfort. Homeowners should also ensure property drainage can handle the heavy 47.1-inch rainfall.
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.