| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 25°F | 41°F | 32°F | 3.3" |
| February | 27°F | 43°F | 34°F | 2.1" |
| March | 38°F | 57°F | 46°F | 4.7" |
| April | 48°F | 70°F | 58°F | 9.5" |
| May | 58°F | 78°F | 67°F | 4.8" |
| June | 66°F | 86°F | 75°F | 2.2" |
| July | 67°F | 87°F | 76°F | 8.0" |
| August | 65°F | 86°F | 75°F | 1.7" |
| September | 57°F | 81°F | 68°F | 5.4" |
| October | 47°F | 70°F | 57°F | 1.8" |
| November | 37°F | 56°F | 45°F | 6.7" |
| December | 30°F | 44°F | 36°F | 2.5" |
| Index | Calhoun | Illinois | National |
| Air quality index | 36 | 41 | 42 |
| Pollution index | 500,004 | 3,148,694 | 2,726,193 |
| Measurement | Total |
| Days measured | 359 |
| Days with good air quality | 328 |
| Days with moderate air quality | 31 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.001% |
| Benzene | 0.020% |
| Carbon Tetrachloride | 0.000% |
| Lead | 0.000% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Claremont, IL | 218 | 36 | 28.0% |
| Parkersburg, IL | 223 | 36 | 28.0% |
| Olney, IL | 8,872 | 36 | 28.0% |
| West Salem, IL | 872 | 36 | 28.0% |
| Sumner, IL | 2,916 | 36 | 28.0% |
| Calhoun, IL | 149 | 36 | 28.0% |
| City | Population | Air Quality Index | National Avg. |
| Calvert, AL | 149 | 42 | 16.0% |
| Rudy, AR | 149 | 36 | 28.0% |
| Blairsburg, IA | 149 | 37 | 26.0% |
| Littleton, IL | 149 | 41 | 18.0% |
| Livingston, KY | 149 | 40 | 20.0% |
| Calhoun, IL | 149 | 36 | 28.0% |
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