Illinois · county records since 1895, through September 2026.
Weather › Illinois › DeKalb County
DeKalb County just had its 5th-warmest September in 132 years, +4° against the usual. DeKalb County's warmest year in 131 on record was 2024, at 52.3° on average.
That is the 1991 to 2020 average for these dates in DeKalb County. The Weather Service forecast fills in below.
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Each bar is a month's average temperature against the usual for that month (1991 to 2020). Ranks compare the same month in every year since 1895.
Rain and melted snow against the usual for each month. The drought reading is NOAA's Palmer index for the county.
| Month | Usual high / low | Usual rain | Warmest | Coldest |
|---|---|---|---|---|
| January | 29° / 14° | 1.7 in | 33.3° 2006 | 5.2° 1912 |
| February | 34° / 18° | 1.7 in | 37.4° 1998 | 9.0° 1936 |
| March | 46° / 27° | 2.3 in | 51.7° 2012 | 21.9° 1960 |
| April | 60° / 37° | 3.7 in | 55.2° 1915 | 39.1° 1907 |
| May | 71° / 49° | 4.6 in | 67.4° 1977 | 51.6° 1907 |
| June | 80° / 58° | 4.8 in | 75.5° 1933 | 62.3° 1916 |
| July | 83° / 62° | 3.9 in | 79.3° 1901 | 66.8° 2009 |
| August | 81° / 60° | 3.9 in | 78.3° 1947 | 63.4° 1915 |
| September | 75° / 53° | 3.5 in | 69.4° 1897 | 56.7° 1918 |
| October | 63° / 41° | 3.1 in | 61.3° 1963 | 41.2° 1925 |
| November | 47° / 30° | 2.5 in | 47.8° 2001 | 29.4° 1951 |
| December | 35° / 20° | 2.0 in | 37.8° 2015 | 12.9° 1963 |
Warmest and coldest are the month's whole-month average temperature, with the year it happened.