| 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 | Mattoon | Illinois | National |
| Air quality index | 40 | 41 | 42 |
| Pollution index | 1,664,370 | 3,148,694 | 2,726,193 |
| Measurement | Total |
| Days measured | 245 |
| Days with good air quality | 224 |
| Days with moderate air quality | 21 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.001% |
| Benzene | 0.040% |
| Carbon Tetrachloride | 0.000% |
| Lead | 0.030% |
| Mercury | 0.003% |
| City | Population | Air Quality Index | National Avg. |
| Windsor, IL | 1,150 | 40 | 20.0% |
| Strasburg, IL | 528 | 40 | 20.0% |
| Stewardson, IL | 710 | 40 | 20.0% |
| Gays, IL | 209 | 40 | 20.0% |
| Toledo, IL | 1,163 | 40 | 20.0% |
| Mattoon, IL | 17,273 | 40 | 20.0% |
| City | Population | Air Quality Index | National Avg. |
| Colonial Heights, VA | 17,283 | 44 | 12.0% |
| Lindenwold, NJ | 17,288 | 51 | 2.0% |
| Taylor, TX | 17,291 | 44 | 12.0% |
| Coalinga, CA | 17,252 | 56 | 12.0% |
| Brenham, TX | 17,297 | 52 | 4.0% |
| Mattoon, IL | 17,273 | 40 | 20.0% |
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