Clay County Climate
Clay County, Illinois
Avg Annual Temp
55.5°F
Annual Precip
47.0"
Annual Snowfall
10.2"
Extreme Heat Days
39.8
days >= 90°F/yr
Monthly Temperature
Precipitation Calendar
Seasonal Overview
National Comparison
Climate Profile
About Clay County Weather
Warmer and wetter than the national median
Clay County is warmer than the national median, boasting an annual average temperature of 55.5°F. Its 47.0 inches of annual precipitation makes it one of the wetter regions in the American Midwest.
Among the warmest spots in Illinois
Ranking well above the state average of 52.8°F, Clay is among the warmest counties in southern Illinois. It also exceeds the state’s average rainfall by over five inches per year.
Outpacing Clinton County in extreme heat
Clay’s 40 extreme heat days per year outpace the 32 days seen in neighboring Clinton County. However, both counties share similar winter profiles with approximately 10 inches of annual snowfall.
Intense summer heat with mild winters
Summer is intense here, with 40 days hitting 90°F or higher and a July average of 77.3°F. Winters are the mildest in this group, with a January average of 30.9°F and just 10.2 inches of snow.
Maximize HVAC efficiency for high heat
Residents should invest in high-efficiency HVAC systems to manage the 40 days of extreme summer heat. Outdoor gear should focus on rain protection given the heavy 47-inch annual precipitation total.
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.