| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 21°F | 37°F | 28°F | 3.7" |
| February | 22°F | 40°F | 30°F | 2.7" |
| March | 34°F | 54°F | 43°F | 3.0" |
| April | 44°F | 67°F | 54°F | 5.7" |
| May | 54°F | 76°F | 64°F | 5.7" |
| June | 62°F | 83°F | 72°F | 5.5" |
| July | 64°F | 85°F | 74°F | 5.1" |
| August | 62°F | 84°F | 72°F | 4.8" |
| September | 55°F | 80°F | 66°F | 4.3" |
| October | 45°F | 67°F | 55°F | 4.9" |
| November | 34°F | 53°F | 43°F | 4.5" |
| December | 27°F | 41°F | 33°F | 5.4" |
| Index | Sidell | Illinois | National |
| Air quality index | 42 | 41 | 42 |
| Pollution index | 9,793,540 | 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 | 0.070% |
| Carbon Tetrachloride | 0.010% |
| Lead | 0.001% |
| Mercury | 0.040% |
| City | Population | Air Quality Index | National Avg. |
| Allerton, IL | 267 | 42 | 16.0% |
| Fithian, IL | 536 | 42 | 16.0% |
| St. Joseph, IL | 4,053 | 42 | 16.0% |
| Fairmount, IL | 540 | 42 | 16.0% |
| Belgium, IL | 383 | 42 | 16.0% |
| Sidell, IL | 492 | 42 | 16.0% |
| City | Population | Air Quality Index | National Avg. |
| Aguilar, CO | 492 | 20 | 60.0% |
| Salem, IA | 492 | 29 | 42.0% |
| Stanhope, IA | 492 | 37 | 26.0% |
| Breckenridge, MO | 492 | 43 | 14.0% |
| Ashland, MS | 492 | 39 | 22.0% |
| Sidell, IL | 492 | 42 | 16.0% |
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