Mercer County Climate

Mercer County, Illinois

JanFebMarAprMayJunJulAugSepOctNovDec50.6°AVG °F

Avg Annual Temp

50.6°F

Annual Precip

37.6"

Annual Snowfall

21.1"

Extreme Heat Days

18.8

days >= 90°F/yr

Monthly Temperature

54.4°F avgJFMAMJJASOND

Precipitation Calendar

Dry
Wet= snowfall
1.5"
1.8"
2.5"
3.8"
5.0"
4.9"
3.6"
3.8"
3.6"
2.8"
2.2"
1.9"
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec

Seasonal Overview

Comfort ZoneSpring39°62°11.3"Summer71°75°12.3"Fall40°66°8.7"Winter23°29°5.3"20°40°60°80°100°

National Comparison

Warmer than 33% of US counties
Wetter than 39% of US counties
More seasonal variation than 81% of US counties

Climate Profile

About Mercer County Weather

A True Four-Season Midwestern Climate

Mercer County's 50.6°F average annual temperature is cooler than the national median. This northwestern Illinois county experiences a pronounced winter season and warm, humid summers.

Cooler and Drier Than Average Illinois

The county's 50.6°F average and 37.6 inches of rain both fall below the Illinois state averages. It represents the cooler, northern-fringe climate of the state's midsection.

Higher Snowfall Than Central Peers

Mercer averages 21.1 inches of snow, significantly more than neighbors like McLean. It enjoys a milder summer than southern counties, with only 19 extreme heat days.

Cold Winters and Manageable Summers

The January average is a cold 22.8°F, and the county sees over 21 inches of snow each year. Summers are warm but rarely oppressive, with 19 days reaching 90°F or higher.

Gear Up for Significant Winter Snow

Invest in a reliable snow shovel or blower to handle the 21.1 inches of annual snowfall. You will also need robust home heating to stay comfortable during the 22.8°F January lows.

Frequently Asked Questions

What is the average temperature in Mercer County?
The average annual temperature in Mercer County, IL is 50.6°F, based on NOAA 30-year climate normals (1991-2020).
How much rain does Mercer County get?
Mercer County receives an average of 37.6 inches of precipitation per year, including both rain and meltwater from snow. This is based on NOAA 30-year climate normals.
Does it snow in Mercer County?
Yes, Mercer County receives an average of 21.1 inches of snowfall per year according to NOAA climate normals.
How hot does Mercer County get in summer?
The average summer temperature (June-August) in Mercer County is 73.1°F. The county experiences an average of 18.8 days per year above 90°F.
How cold are winters in Mercer County?
The average winter temperature (December-February) in Mercer County is 26.1°F. January, typically the coldest month, averages 22.8°F.

Track your own weather in Mercer County

Ambient Weather personal weather stations give you hyperlocal climate data.

Shop Weather Stations →

Sponsored

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.

Explore more data for Mercer County

TaxCost of LivingComing SoonCrime RateIncomeComing SoonHealthSchoolsRiskWaterCounty Score