| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 16°F | 31°F | 23°F | 2.8" |
| February | 17°F | 32°F | 24°F | 2.8" |
| March | 30°F | 47°F | 37°F | 4.6" |
| April | 39°F | 61°F | 49°F | 5.8" |
| May | 50°F | 72°F | 60°F | 5.3" |
| June | 59°F | 80°F | 69°F | 5.6" |
| July | 63°F | 82°F | 72°F | 5.8" |
| August | 61°F | 81°F | 70°F | 5.9" |
| September | 54°F | 75°F | 63°F | 3.7" |
| October | 43°F | 63°F | 52°F | 5.8" |
| November | 32°F | 49°F | 39°F | 4.0" |
| December | 21°F | 34°F | 27°F | 3.1" |
| Index | DeKalb | Illinois | National |
| Air quality index | 42 | 41 | 42 |
| Pollution index | 1,874,490 | 3,148,694 | 2,726,193 |
| Measurement | Total |
| Days measured | 341 |
| Days with good air quality | 240 |
| Days with moderate air quality | 100 |
| Days w/ poor A.Q. for sensitive groups | 1 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.002% |
| Benzene | 0.030% |
| Carbon Tetrachloride | 0.010% |
| Lead | 0.010% |
| Mercury | 0.010% |
| City | Population | Air Quality Index | National Avg. |
| Shabbona, IL | 937 | 0 | 100.0% |
| Big Rock, IL | 1,271 | 0 | 100.0% |
| Waterman, IL | 1,738 | 0 | 100.0% |
| Kaneville, IL | 518 | 0 | 100.0% |
| Hinckley, IL | 2,190 | 0 | 100.0% |
| DeKalb, IL | 42,961 | 42 | 16.0% |
| City | Population | Air Quality Index | National Avg. |
| Goose Creek, SC | 42,944 | 38 | 24.0% |
| Fond du Lac, WI | 42,944 | 36 | 28.0% |
| Winter Haven, FL | 42,933 | 36 | 28.0% |
| Freeport, NY | 42,993 | 51 | 2.0% |
| Vaudreuil-Dorion, QC | 42,920 | n/a | |
| DeKalb, IL | 42,961 | 42 | 16.0% |
Here are the best places to live in Illinois
Safest States In The US
See the best places to live in DeKalb
Check out the 10 most dangerous cities in Illinois