| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 17°F | 32°F | 24°F | 3.1" |
| February | 18°F | 34°F | 26°F | 3.0" |
| March | 31°F | 49°F | 39°F | 5.2" |
| April | 40°F | 62°F | 50°F | 4.8" |
| May | 51°F | 73°F | 61°F | 5.9" |
| June | 60°F | 82°F | 70°F | 6.7" |
| July | 64°F | 84°F | 73°F | 4.1" |
| August | 62°F | 82°F | 71°F | 7.7" |
| September | 55°F | 76°F | 65°F | 3.2" |
| October | 44°F | 64°F | 53°F | 7.3" |
| November | 33°F | 50°F | 41°F | 3.9" |
| December | 22°F | 36°F | 29°F | 3.7" |
| Index | Darien | 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. |
| Plainfield, IL | 44,857 | 55 | 10.0% |
| Broadview, IL | 7,677 | 55 | 10.0% |
| Forest Park, IL | 13,808 | 55 | 10.0% |
| Country Club Hills, IL | 16,564 | 55 | 10.0% |
| Crestwood, IL | 10,762 | 55 | 10.0% |
| Darien, IL | 21,843 | 55 | 10.0% |
| City | Population | Air Quality Index | National Avg. |
| Geneva, IL | 21,843 | 55 | 10.0% |
| Linda, CA | 21,842 | 44 | 12.0% |
| Shelbyville, TN | 21,841 | 31 | 38.0% |
| Rose Hill, VA | 21,846 | 47 | 6.0% |
| Lexington, SC | 21,847 | 43 | 14.0% |
| Darien, IL | 21,843 | 55 | 10.0% |
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