Johnson County Climate
Johnson County, Illinois
NOAA NCEI 1991-2020 Climate NormalsAvg Annual Temp
57.9°F
Annual Precip
49.4"
Annual Snowfall
7.2"
Extreme Heat Days
41
days >= 90°F/yr
Monthly Temperature
Precipitation Calendar
Growing Season & Gardening
7a
Minimum winter temperature range for plant survival
Seasonal Overview
National Comparison
7-Day Outlook
Forecast
Current Conditions
Air Quality
Safety
Weather Alerts
Climate Advisory: Johnson County
Climate Verdict
Johnson County has a mild, with an average annual temperature of 57.9°F, moderately wet with 49.4 inches of annual precipitation, occasional hot days — 41.3 per year above 90°F, light snow averaging 7.2 inches per year. This climate profile shapes everything from energy costs to outdoor recreation opportunities.
Seasonal Breakdown
Winters are cold, with January averaging 34.6°F. summers are warm — July averages 78.9°F. The 44°F seasonal variation provides noticeable but manageable change.
Outdoor & Gardening Guidance
The moderate temperatures support hiking, cycling, and camping comfortably in spring, summer, and fall.
Regional Context
Johnson County is 5.1°F warmer than the Illinois statewide average of 52.8°F, it is also noticeably wetter, receiving 7.6 inches more precipitation than the state average.
Frequently Asked Questions
What is the average temperature in Johnson County?
How much rain does Johnson County get?
Does it snow in Johnson County?
How hot does Johnson County get in summer?
How cold are winters in Johnson County?
Track your own weather in Johnson County
Ambient Weather personal weather stations give you hyperlocal climate data.
Sponsored
Data sources: NOAA National Centers for Environmental Information (NCEI), U.S. Climate Normals 1991-2020. Forecast and alert data from National Weather Service API. Air quality data from Open-Meteo.
Climate normals are 30-year averages of weather variables. Station data is aggregated to county level. Forecasts and alerts are fetched live and may change frequently. Data is informational only — not a substitute for official National Weather Service forecasts or emergency weather warnings.