| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 21°F | 39°F | 29°F | 3.5" |
| February | 23°F | 41°F | 31°F | 3.2" |
| March | 36°F | 56°F | 44°F | 3.6" |
| April | 46°F | 68°F | 56°F | 7.4" |
| May | 56°F | 76°F | 65°F | 7.6" |
| June | 64°F | 84°F | 74°F | 10.4" |
| July | 67°F | 87°F | 76°F | 8.6" |
| August | 65°F | 87°F | 75°F | 6.1" |
| September | 58°F | 81°F | 68°F | 8.5" |
| October | 46°F | 68°F | 56°F | 5.6" |
| November | 36°F | 55°F | 45°F | 5.5" |
| December | 27°F | 42°F | 33°F | 6.1" |
| Index | Milton | Illinois | National |
| Air quality index | 41 | 41 | 42 |
| Pollution index | 2,458,180 | 3,148,694 | 2,726,193 |
| Measurement | Total |
| Days measured | 241 |
| Days with good air quality | 208 |
| Days with moderate air quality | 33 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.002% |
| Benzene | 0.020% |
| Carbon Tetrachloride | 0.001% |
| Lead | 0.120% |
| Mercury | 0.330% |
| City | Population | Air Quality Index | National Avg. |
| Glasgow, IL | 93 | 40 | 20.0% |
| Chapin, IL | 536 | 40 | 20.0% |
| Roodhouse, IL | 1,656 | 40 | 20.0% |
| Hillview, IL | 161 | 40 | 20.0% |
| White Hall, IL | 2,356 | 40 | 20.0% |
| Milton, IL | 317 | 41 | 18.0% |
| City | Population | Air Quality Index | National Avg. |
| Gillsville, GA | 317 | 37 | 26.0% |
| Maunaloa, HI | 317 | 30 | 40.0% |
| Granville, IA | 317 | 35 | 30.0% |
| Mystic, IA | 317 | 39 | 22.0% |
| Ute, IA | 317 | 35 | 30.0% |
| Milton, IL | 317 | 41 | 18.0% |
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