| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 25°F | 39°F | 31°F | 6.1" |
| February | 23°F | 37°F | 29°F | 2.4" |
| March | 37°F | 55°F | 45°F | 4.1" |
| April | 44°F | 65°F | 53°F | 3.9" |
| May | 55°F | 77°F | 65°F | 2.6" |
| June | 64°F | 85°F | 75°F | 4.7" |
| July | 65°F | 86°F | 75°F | 8.2" |
| August | 68°F | 88°F | 77°F | 7.2" |
| September | 59°F | 83°F | 71°F | 8.1" |
| October | 49°F | 69°F | 58°F | 8.2" |
| November | 36°F | 54°F | 44°F | 3.6" |
| December | 25°F | 38°F | 31°F | 2.6" |
| Index | Humboldt | Illinois | National |
| Air quality index | 42 | 41 | 42 |
| Pollution index | 1,494,160 | 3,148,694 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 281 |
| Days with moderate air quality | 84 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.010% |
| Benzene | 0.040% |
| Carbon Tetrachloride | 0.290% |
| Lead | 0.010% |
| Mercury | 0.010% |
| City | Population | Air Quality Index | National Avg. |
| Windsor, IL | 1,150 | 40 | 20.0% |
| Charleston, IL | 20,141 | 40 | 20.0% |
| Gays, IL | 209 | 40 | 20.0% |
| Mattoon, IL | 17,273 | 40 | 20.0% |
| Lerna, IL | 251 | 40 | 20.0% |
| Humboldt, IL | 446 | 42 | 16.0% |
| City | Population | Air Quality Index | National Avg. |
| Hamilton Branch, CA | 446 | 46 | 8.0% |
| Utica, KY | 446 | 43 | 14.0% |
| Edgefield, LA | 446 | 39 | 22.0% |
| Georgetown, LA | 446 | 30 | 40.0% |
| White Pine, MI | 446 | 8 | 84.0% |
| Humboldt, IL | 446 | 42 | 16.0% |
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