| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 18°F | 34°F | 25°F | 2.5" |
| February | 19°F | 36°F | 27°F | 2.8" |
| March | 31°F | 50°F | 39°F | 4.5" |
| April | 41°F | 63°F | 51°F | 4.9" |
| May | 50°F | 73°F | 61°F | 4.7" |
| June | 60°F | 83°F | 71°F | 5.4" |
| July | 64°F | 85°F | 74°F | 5.7" |
| August | 62°F | 83°F | 72°F | 6.8" |
| September | 55°F | 77°F | 65°F | 5.4" |
| October | 44°F | 64°F | 53°F | 5.7" |
| November | 33°F | 51°F | 41°F | 4.9" |
| December | 23°F | 37°F | 30°F | 3.7" |
| Index | Joliet | Illinois | National |
| Air quality index | 55 | 41 | 42 |
| Pollution index | 1,558,070 | 3,148,694 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 121 |
| Days with moderate air quality | 227 |
| Days w/ poor A.Q. for sensitive groups | 16 |
| Days with unhealthy air quality | 1 |
| Pollutant | Total |
| Arsenic | 0.010% |
| Benzene | 0.010% |
| Carbon Tetrachloride | 0.070% |
| Lead | 0.090% |
| Mercury | 0.010% |
| City | Population | Air Quality Index | National Avg. |
| Channahon, IL | 13,281 | 0 | 100.0% |
| Wilmington village, IL | 144 | 0 | 100.0% |
| Minooka, IL | 11,069 | 0 | 100.0% |
| Wilmington, IL | 5,883 | 0 | 100.0% |
| Montgomery, IL | 19,515 | 0 | 100.0% |
| Joliet, IL | 147,323 | 55 | 10.0% |
| City | Population | Air Quality Index | National Avg. |
| Rockford, IL | 147,441 | 42 | 16.0% |
| Naperville, IL | 147,734 | 55 | 10.0% |
| Guelph, ON | 147,931 | n/a | |
| Bellevue, WA | 146,145 | 45 | 10.0% |
| Killeen, TX | 148,573 | 42 | 16.0% |
| Joliet, IL | 147,323 | 55 | 10.0% |
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