| 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 | McHenry | Illinois | National |
| Air quality index | 39 | 41 | 42 |
| Pollution index | 543,516 | 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 | 0.000% |
| 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% |
| Hebron, IL | 1,730 | 37 | 26.0% |
| Bloomfield, WI | 4,725 | 37 | 26.0% |
| Fontana-on-Geneva Lake, WI | 1,518 | 37 | 26.0% |
| Grayslake, IL | 20,482 | 39 | 22.0% |
| McHenry, IL | 26,889 | 39 | 22.0% |
| City | Population | Air Quality Index | National Avg. |
| Lindenhurst, NY | 26,885 | 51 | 2.0% |
| Temple Terrace, FL | 26,901 | 43 | 14.0% |
| Ilchester, MD | 26,873 | 46 | 8.0% |
| Carrollton, GA | 26,857 | 52 | 4.0% |
| Shoreview, MN | 26,922 | 46 | 8.0% |
| McHenry, IL | 26,889 | 39 | 22.0% |
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