| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 20°F | 38°F | 29°F | 2.1" |
| February | 22°F | 41°F | 31°F | 1.9" |
| March | 34°F | 56°F | 44°F | 2.9" |
| April | 44°F | 68°F | 56°F | 4.3" |
| May | 54°F | 77°F | 65°F | 4.5" |
| June | 64°F | 86°F | 74°F | 5.5" |
| July | 66°F | 88°F | 77°F | 4.3" |
| August | 64°F | 86°F | 75°F | 3.2" |
| September | 57°F | 81°F | 68°F | 3.7" |
| October | 46°F | 69°F | 56°F | 3.7" |
| November | 36°F | 55°F | 45°F | 2.5" |
| December | 26°F | 41°F | 33°F | 2.8" |
| Index | Chatham | Illinois | National |
| Air quality index | 40 | 41 | 42 |
| Pollution index | 5,136,080 | 3,148,694 | 2,726,193 |
| Measurement | Total |
| Days measured | 360 |
| Days with good air quality | 287 |
| Days with moderate air quality | 73 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.010% |
| Benzene | 0.090% |
| Carbon Tetrachloride | 0.010% |
| Lead | 0.390% |
| Mercury | 0.020% |
| City | Population | Air Quality Index | National Avg. |
| Berlin, IL | 182 | 40 | 20.0% |
| Divernon, IL | 1,194 | 40 | 20.0% |
| Loami, IL | 1,053 | 40 | 20.0% |
| Southern View, IL | 1,605 | 40 | 20.0% |
| Modesto, IL | 222 | 40 | 20.0% |
| Chatham, IL | 13,231 | 40 | 20.0% |
| City | Population | Air Quality Index | National Avg. |
| Baker, LA | 13,233 | 45 | 10.0% |
| Glenn Heights, TX | 13,228 | 51 | 2.0% |
| McFarland, CA | 13,244 | 67 | 34.0% |
| Lahaina, HI | 13,216 | 15 | 70.0% |
| Bedford, IN | 13,246 | 42 | 16.0% |
| Chatham, IL | 13,231 | 40 | 20.0% |
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