Average Rainfall for Illinois in August
The tables below give monthly averages for rainfall during August at cities in Illinois.
Each place has a total for the amount of precipitation it usually receives this month. There is also a count of the number of days with wet weather, when precipitation amounts to 0.01 inches (0.25 millimetres) or more.
The rainfall totals are averages based on weather data collected from 1991 to 2020 for the US National Centers for Environmental Information.
You can jump to a separate table for each region of the state: Chicago Area, Northern Illinois, Central Illinois and Southern Illinois.
Chicago Area
| Days | Place | Inches | Millimetres |
|---|---|---|---|
| 9 | Aurora | 3.9 | 98 |
| 10 | Chicago Botanical Garden | 4.2 | 106 |
| 9 | Chicago Midway Airport | 4.1 | 104 |
| 9 | Chicago O'Hare Airport | 4.3 | 108 |
| 10 | Elgin | 4.3 | 110 |
| 9 | Joliet | 4.0 | 101 |
| 9 | Rochelle | 3.9 | 100 |
Northern Illinois
| Days | Place | Inches | Millimetres |
|---|---|---|---|
| 9 | DeKalb | 4.1 | 103 |
| 8 | Dixon | 4.2 | 106 |
| 10 | Freeport | 4.2 | 107 |
| 9 | Moline | 4.0 | 101 |
| 9 | Rockford | 4.2 | 106 |
| 13 | Waukegan | 3.6 | 91 |
Central Illinois
| Days | Place | Inches | Millimetres |
|---|---|---|---|
| 7 | Alton | 3.3 | 84 |
| 8 | Bloomington | 3.8 | 95 |
| 8 | Cahokia | 3.1 | 78 |
| 9 | Champaign | 3.5 | 90 |
| 8 | Charleston | 2.9 | 75 |
| 9 | Danville | 3.3 | 84 |
| 7 | Decatur | 3.5 | 89 |
| 9 | Kankakee | 3.9 | 98 |
| 9 | Ottawa | 3.7 | 94 |
| 8 | Peoria | 3.3 | 84 |
| 8 | Quincy | 3.9 | 100 |
| 8 | Springfield | 3.4 | 86 |
Southern Illinois
| Days | Place | Inches | Millimetres |
|---|---|---|---|
| 7 | Belleville | 3.9 | 100 |
| 9 | Carbondale | 3.2 | 80 |
| 8 | Mt Vernon | 3.3 | 85 |
Reference
NOAA National Centers for Environmental Information (NCEI). Climate Normals.