| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 20°F | 34°F | 26°F | 1.9" |
| February | 21°F | 36°F | 28°F | 1.6" |
| March | 33°F | 49°F | 40°F | 2.4" |
| April | 42°F | 62°F | 51°F | 3.6" |
| May | 52°F | 73°F | 61°F | 4.3" |
| June | 63°F | 82°F | 72°F | 4.6" |
| July | 68°F | 86°F | 76°F | 3.5" |
| August | 67°F | 83°F | 75°F | 5.1" |
| September | 60°F | 77°F | 68°F | 2.8" |
| October | 48°F | 65°F | 55°F | 3.9" |
| November | 36°F | 51°F | 43°F | 2.2" |
| December | 25°F | 37°F | 31°F | 2.2" |
| Index | McCook | Illinois | National |
| Air quality index | 55 | 41 | 42 |
| Pollution index | 14,981,300 | 3,148,694 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 121 |
| Days with moderate air quality | 227 |
| Days w/ poor A.Q. for sensitive groups | 16 |
| Days with unhealthy air quality | 1 |
| Pollutant | Total |
| Arsenic | 0.010% |
| Benzene | 0.140% |
| Carbon Tetrachloride | 0.030% |
| Lead | 0.020% |
| Mercury | 0.010% |
| City | Population | Air Quality Index | National Avg. |
| Berwyn, IL | 54,850 | 55 | 10.0% |
| Cicero, IL | 81,471 | 55 | 10.0% |
| Oak Park, IL | 52,102 | 55 | 10.0% |
| Burbank, IL | 28,447 | 55 | 10.0% |
| Harvey, IL | 24,295 | 55 | 10.0% |
| McCook, IL | 317 | 55 | 10.0% |
| 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% |
| McCook, IL | 317 | 55 | 10.0% |
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