| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 21°F | 34°F | 27°F | 4.6" |
| February | 20°F | 32°F | 25°F | 1.8" |
| March | 30°F | 49°F | 39°F | 2.6" |
| April | 39°F | 60°F | 49°F | 4.5" |
| May | 50°F | 72°F | 60°F | 3.5" |
| June | 63°F | 84°F | 73°F | 3.8" |
| July | 65°F | 84°F | 74°F | 5.4" |
| August | 67°F | 83°F | 75°F | 12.8" |
| September | 59°F | 80°F | 69°F | 6.7" |
| October | 49°F | 66°F | 57°F | 1.7" |
| November | 33°F | 50°F | 41°F | 2.4" |
| December | 19°F | 32°F | 26°F | 1.7" |
| Index | Northfield | Illinois | National |
| Air quality index | 55 | 41 | 42 |
| Pollution index | 3,795,410 | 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 | 0.030% |
| Benzene | 0.050% |
| Carbon Tetrachloride | 0.010% |
| Lead | 0.003% |
| Mercury | 0.310% |
| City | Population | Air Quality Index | National Avg. |
| Mundelein, IL | 31,574 | 39 | 22.0% |
| North Chicago, IL | 29,967 | 39 | 22.0% |
| Knollwood, IL | 1,684 | 39 | 22.0% |
| Libertyville, IL | 20,300 | 39 | 22.0% |
| Green Oaks, IL | 3,882 | 39 | 22.0% |
| Northfield, IL | 5,678 | 55 | 10.0% |
| City | Population | Air Quality Index | National Avg. |
| Montrose-Ghent, OH | 5,677 | 43 | 14.0% |
| Trenton, MO | 5,679 | 43 | 14.0% |
| Lackland AFB, TX | 5,679 | 49 | 2.0% |
| Sharon Hill, PA | 5,680 | 51 | 2.0% |
| Eastwood, MI | 5,675 | 38 | 24.0% |
| Northfield, IL | 5,678 | 55 | 10.0% |
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