| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 28°F | 43°F | 34°F | 9.8" |
| February | 26°F | 45°F | 34°F | 4.7" |
| March | 38°F | 60°F | 48°F | 2.9" |
| April | 45°F | 68°F | 56°F | 5.6" |
| May | 56°F | 79°F | 67°F | 3.7" |
| June | 65°F | 88°F | 76°F | 7.6" |
| July | 67°F | 88°F | 77°F | 12.3" |
| August | 70°F | 93°F | 80°F | 7.2" |
| September | 61°F | 85°F | 72°F | 16.1" |
| October | 49°F | 72°F | 59°F | 7.5" |
| November | 38°F | 59°F | 47°F | 11.9" |
| December | 27°F | 42°F | 33°F | 2.9" |
| Index | Fayetteville | Illinois | National |
| Air quality index | 54 | 41 | 42 |
| Pollution index | 1,232,920 | 3,148,694 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 134 |
| Days with moderate air quality | 221 |
| Days w/ poor A.Q. for sensitive groups | 8 |
| Days with unhealthy air quality | 2 |
| Pollutant | Total |
| Arsenic | 0.170% |
| Benzene | 0.030% |
| Carbon Tetrachloride | 0.000% |
| Lead | 0.010% |
| Mercury | 0.290% |
| City | Population | Air Quality Index | National Avg. |
| Tilden, IL | 961 | 43 | 14.0% |
| Okawville, IL | 1,469 | 43 | 14.0% |
| Germantown, IL | 1,279 | 43 | 14.0% |
| Coulterville, IL | 881 | 43 | 14.0% |
| Rentchler, IL | 4 | 54 | 8.0% |
| Fayetteville, IL | 438 | 54 | 8.0% |
| City | Population | Air Quality Index | National Avg. |
| Calion, AR | 438 | 35 | 30.0% |
| Shaver Lake, CA | 438 | 60 | 20.0% |
| Lake City, CO | 438 | 44 | 12.0% |
| Moreland, GA | 438 | 52 | 4.0% |
| Alleman, IA | 438 | 37 | 26.0% |
| Fayetteville, IL | 438 | 54 | 8.0% |
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