| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 16°F | 32°F | 24°F | 1.4" |
| February | 17°F | 33°F | 25°F | 1.5" |
| March | 28°F | 45°F | 36°F | 2.6" |
| April | 37°F | 57°F | 46°F | 4.1" |
| May | 47°F | 68°F | 57°F | 3.7" |
| June | 57°F | 77°F | 67°F | 4.5" |
| July | 63°F | 82°F | 72°F | 4.4" |
| August | 62°F | 80°F | 71°F | 3.7" |
| September | 55°F | 73°F | 64°F | 3.3" |
| October | 44°F | 62°F | 52°F | 3.4" |
| November | 33°F | 49°F | 40°F | 2.0" |
| December | 22°F | 36°F | 29°F | 2.5" |
| Index | Zion | Illinois | National |
| Air quality index | 39 | 41 | 42 |
| Pollution index | 3,131,700 | 3,148,694 | 2,726,193 |
| Measurement | Total |
| Days measured | 203 |
| Days with good air quality | 174 |
| Days with moderate air quality | 28 |
| Days w/ poor A.Q. for sensitive groups | 1 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.010% |
| Benzene | 0.030% |
| Carbon Tetrachloride | 0.010% |
| Lead | 0.004% |
| Mercury | 0.360% |
| City | Population | Air Quality Index | National Avg. |
| Grandwood Park, IL | 5,114 | 39 | 22.0% |
| Mundelein, IL | 31,574 | 39 | 22.0% |
| Old Mill Creek, IL | 200 | 39 | 22.0% |
| Round Lake Heights, IL | 3,009 | 39 | 22.0% |
| Green Oaks, IL | 3,882 | 39 | 22.0% |
| Zion, IL | 23,677 | 39 | 22.0% |
| City | Population | Air Quality Index | National Avg. |
| Newberg, OR | 23,676 | 38 | 24.0% |
| Windsor, CO | 23,679 | 45 | 10.0% |
| Searcy, AR | 23,673 | 45 | 10.0% |
| North Haven, CT | 23,665 | 41 | 18.0% |
| Muscatine, IA | 23,661 | 32 | 36.0% |
| Zion, IL | 23,677 | 39 | 22.0% |
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