Illinois weather by county

Illinois in September 2026

• 102 of 102 counties ran at least 1° warmer than usual in September 2026, and 0 ran at least 1° cooler.
• Warmest against its own records: Adams County (1st-warmest September of 132). Even the least warm, Boone County, had its 10th-warmest.
• Wettest September against its records: Lee County, 9.1 inches (6th-wettest).
• 19 of 102 counties were in moderate drought or worse on NOAA's Palmer reading for September.
• Since 1970 the state's counties have warmed about 0.5° per decade on average, Carroll County the most at 0.6°.

This week's forecast against the usual, and every month since 1895, for all 102 counties in Illinois. 102 had a top-10 warm September in 2026.

• Adams County 1st warmest Sep
• Alexander County 1st warmest Sep
• Bond County 1st warmest Sep
• Boone County 10th warmest Sep
• Brown County 1st warmest Sep
• Bureau County 4th warmest Sep
• Calhoun County 1st warmest Sep
• Carroll County 6th warmest Sep
• Cass County 1st warmest Sep
• Champaign County 1st warmest Sep
• Christian County 1st warmest Sep
• Clark County 1st warmest Sep
• Clay County 1st warmest Sep
• Clinton County 1st warmest Sep
• Coles County 1st warmest Sep
• Cook County 7th warmest Sep
• Crawford County 1st warmest Sep
• Cumberland County 1st warmest Sep
• De Witt County 1st warmest Sep
• DeKalb County 5th warmest Sep
• Douglas County 1st warmest Sep
• DuPage County 6th warmest Sep
• Edgar County 1st warmest Sep
• Edwards County 1st warmest Sep
• Effingham County 1st warmest Sep
• Fayette County 1st warmest Sep
• Ford County 1st warmest Sep
• Franklin County 1st warmest Sep
• Fulton County 3rd warmest Sep
• Gallatin County 1st warmest Sep
• Greene County 1st warmest Sep
• Grundy County 1st warmest Sep
• Hamilton County 1st warmest Sep
• Hancock County 3rd warmest Sep
• Hardin County 2nd warmest Sep
• Henderson County 4th warmest Sep
• Henry County 3rd warmest Sep
• Iroquois County 1st warmest Sep
• Jackson County 1st warmest Sep
• Jasper County 1st warmest Sep
• Jefferson County 1st warmest Sep
• Jersey County 1st warmest Sep
• Jo Daviess County 5th warmest Sep
• Johnson County 1st warmest Sep
• Kane County 3rd warmest Sep
• Kankakee County 1st warmest Sep
• Kendall County 3rd warmest Sep
• Knox County 3rd warmest Sep
• Lake County 8th warmest Sep
• LaSalle County 6th warmest Sep
• Lawrence County 1st warmest Sep
• Lee County 9th warmest Sep
• Livingston County 1st warmest Sep
• Logan County 1st warmest Sep
• Macon County 1st warmest Sep
• Macoupin County 1st warmest Sep
• Madison County 1st warmest Sep
• Marion County 1st warmest Sep
• Marshall County 1st warmest Sep
• Mason County 1st warmest Sep
• Massac County 1st warmest Sep
• McDonough County 4th warmest Sep
• McHenry County 8th warmest Sep
• McLean County 1st warmest Sep
• Menard County 1st warmest Sep
• Mercer County 1st warmest Sep
• Monroe County 1st warmest Sep
• Montgomery County 1st warmest Sep
• Morgan County 1st warmest Sep
• Moultrie County 1st warmest Sep
• Ogle County 9th warmest Sep
• Peoria County 2nd warmest Sep
• Perry County 1st warmest Sep
• Piatt County 1st warmest Sep
• Pike County 1st warmest Sep
• Pope County 1st warmest Sep
• Pulaski County 1st warmest Sep
• Putnam County 3rd warmest Sep
• Randolph County 1st warmest Sep
• Richland County 1st warmest Sep
• Rock Island County 2nd warmest Sep
• Saline County 1st warmest Sep
• Sangamon County 1st warmest Sep
• Schuyler County 1st warmest Sep
• Scott County 1st warmest Sep
• Shelby County 1st warmest Sep
• St. Clair County 1st warmest Sep
• Stark County 2nd warmest Sep
• Stephenson County 8th warmest Sep
• Tazewell County 1st warmest Sep
• Union County 1st warmest Sep
• Vermilion County 2nd warmest Sep
• Wabash County 1st warmest Sep
• Warren County 4th warmest Sep
• Washington County 1st warmest Sep
• Wayne County 1st warmest Sep
• White County 1st warmest Sep
• Whiteside County 5th warmest Sep
• Will County 2nd warmest Sep
• Williamson County 1st warmest Sep
• Winnebago County 8th warmest Sep
• Woodford County 1st warmest Sep

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