| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 21°F | 39°F | 29°F | 2.6" |
| February | 22°F | 41°F | 31°F | 2.0" |
| March | 34°F | 56°F | 44°F | 3.3" |
| April | 44°F | 68°F | 55°F | 5.8" |
| May | 53°F | 76°F | 65°F | 4.3" |
| June | 63°F | 85°F | 73°F | 6.3" |
| July | 64°F | 87°F | 75°F | 4.5" |
| August | 62°F | 86°F | 74°F | 2.3" |
| September | 55°F | 80°F | 67°F | 2.9" |
| October | 44°F | 68°F | 55°F | 3.5" |
| November | 33°F | 55°F | 43°F | 2.7" |
| December | 26°F | 43°F | 34°F | 3.4" |
| Index | Marshall | Illinois | National |
| Air quality index | 45 | 41 | 42 |
| Pollution index | 1,664,370 | 3,148,694 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 237 |
| Days with moderate air quality | 127 |
| Days w/ poor A.Q. for sensitive groups | 1 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.001% |
| Benzene | 0.040% |
| Carbon Tetrachloride | 0.000% |
| Lead | 0.030% |
| Mercury | 0.003% |
| City | Population | Air Quality Index | National Avg. |
| West Terre Haute, IN | 2,193 | 45 | 10.0% |
| Shepardsville, IN | 117 | 45 | 10.0% |
| West Union, IL | 241 | 45 | 10.0% |
| Dresser, IN | 37 | 45 | 10.0% |
| Kansas, IL | 771 | 45 | 10.0% |
| Marshall, IL | 3,615 | 45 | 10.0% |
| City | Population | Air Quality Index | National Avg. |
| Wyldwood, TX | 3,615 | 44 | 12.0% |
| Wildwood Lake, TN | 3,614 | 1 | 98.0% |
| Wills Point, TX | 3,614 | 51 | 2.0% |
| Saint-Adolphe-d'Howard, QC | 3,614 | n/a | |
| Lake Clarke Shores, FL | 3,616 | 36 | 28.0% |
| Marshall, IL | 3,615 | 45 | 10.0% |
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