| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 17°F | 37°F | 26°F | 2.3" |
| February | 18°F | 39°F | 28°F | 2.1" |
| March | 31°F | 54°F | 42°F | 3.1" |
| April | 41°F | 67°F | 54°F | 4.7" |
| May | 51°F | 77°F | 64°F | 4.4" |
| June | 62°F | 85°F | 73°F | 5.4" |
| July | 65°F | 88°F | 76°F | 3.4" |
| August | 64°F | 86°F | 74°F | 3.5" |
| September | 56°F | 81°F | 68°F | 4.1" |
| October | 44°F | 68°F | 55°F | 3.4" |
| November | 33°F | 55°F | 43°F | 2.9" |
| December | 22°F | 39°F | 30°F | 2.7" |
| Index | Mackinaw | Illinois | National |
| Air quality index | 41 | 41 | 42 |
| Pollution index | 672,031 | 3,148,694 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 285 |
| Days with moderate air quality | 78 |
| Days w/ poor A.Q. for sensitive groups | 2 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.001% |
| Benzene | 0.030% |
| Carbon Tetrachloride | 0.000% |
| Lead | 0.001% |
| Mercury | 0.020% |
| City | Population | Air Quality Index | National Avg. |
| East Peoria, IL | 22,615 | 41 | 18.0% |
| Marquette Heights, IL | 2,742 | 41 | 18.0% |
| Peoria, IL | 112,644 | 41 | 18.0% |
| Creve Coeur, IL | 5,074 | 41 | 18.0% |
| Delavan, IL | 1,708 | 41 | 18.0% |
| Mackinaw, IL | 1,970 | 41 | 18.0% |
| City | Population | Air Quality Index | National Avg. |
| Hagerstown, IN | 1,970 | 28 | 44.0% |
| Bristol, NH | 1,970 | 31 | 38.0% |
| Nambe, NM | 1,970 | 41 | 18.0% |
| Watts Mills, SC | 1,970 | 44 | 12.0% |
| North Puyallup, WA | 1,970 | 45 | 10.0% |
| Mackinaw, IL | 1,970 | 41 | 18.0% |
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