| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 18°F | 33°F | 25°F | 1.1" |
| February | 19°F | 34°F | 26°F | 1.4" |
| March | 30°F | 48°F | 38°F | 1.8" |
| April | 39°F | 60°F | 49°F | 2.7" |
| May | 49°F | 71°F | 60°F | 3.6" |
| June | 60°F | 81°F | 69°F | 4.7" |
| July | 65°F | 85°F | 74°F | 4.0" |
| August | 64°F | 83°F | 73°F | 4.4" |
| September | 56°F | 76°F | 66°F | 2.7" |
| October | 45°F | 64°F | 54°F | 3.2" |
| November | 34°F | 50°F | 42°F | 1.7" |
| December | 23°F | 37°F | 30°F | 2.0" |
| Index | Cary | Illinois | National |
| Air quality index | 55 | 41 | 42 |
| Pollution index | 543,516 | 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 | 0.000% |
| Benzene | 0.004% |
| Carbon Tetrachloride | 0.000% |
| Lead | 0.000% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Greenwood, IL | 352 | 37 | 26.0% |
| Gages Lake, IL | 9,939 | 39 | 22.0% |
| Third Lake, IL | 1,160 | 39 | 22.0% |
| Holiday Hills, IL | 653 | 39 | 22.0% |
| McHenry, IL | 26,889 | 39 | 22.0% |
| Cary, IL | 17,926 | 55 | 10.0% |
| City | Population | Air Quality Index | National Avg. |
| Arroyo Grande, CA | 17,924 | 46 | 8.0% |
| Beltsville, MD | 17,922 | 47 | 6.0% |
| Sainte-Sophie, QC | 17,917 | n/a | |
| Sheridan, WY | 17,938 | 39 | 22.0% |
| Lenoir, NC | 17,909 | 43 | 14.0% |
| Cary, IL | 17,926 | 55 | 10.0% |
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