| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 18°F | 33°F | 25°F | 3.9" |
| February | 18°F | 35°F | 26°F | 2.3" |
| March | 31°F | 50°F | 39°F | 4.3" |
| April | 40°F | 63°F | 50°F | 8.4" |
| May | 51°F | 74°F | 62°F | 6.0" |
| June | 61°F | 82°F | 71°F | 5.7" |
| July | 63°F | 84°F | 73°F | 9.0" |
| August | 62°F | 82°F | 71°F | 5.4" |
| September | 54°F | 77°F | 65°F | 3.7" |
| October | 44°F | 65°F | 53°F | 7.1" |
| November | 33°F | 51°F | 41°F | 4.0" |
| December | 22°F | 37°F | 29°F | 3.0" |
| Index | Sheridan | Illinois | National |
| Air quality index | 1 | 41 | 50 |
| Pollution index | 1,874,490 | 3,347,295 | 5,066,862 |
| Measurement | Total |
| Days measured | 351 |
| Days with good air quality | 351 |
| Days with moderate air quality | |
| Days w/ poor A.Q. for sensitive groups | |
| Days with unhealthy air quality |
| Pollutant | Total |
| Arsenic | 0.002% |
| Benzene | 0.030% |
| Carbon Tetrachloride | 0.010% |
| Lead | 0.010% |
| Mercury | 0.010% |
| City, State | Population | Air Quality Index | National Avg. |
| Earlville, IL | 1,672 | 1 | 98% |
| Marseilles, IL | 4,892 | 1 | 98% |
| Naplate, IL | 441 | 1 | 98% |
| Sandwich, IL | 7,491 | 1 | 98% |
| Lake Holiday, IL | 4,718 | 1 | 98% |
| Sheridan, IL | 2,543 | 1 | 98% |
| City, State | Population | Air Quality Index | National Avg. |
| Williamsburg, OH | 2,543 | 54 | 8% |
| Evansburg, PA | 2,543 | 57 | 14% |
| Imperial, PA | 2,543 | 56 | 12% |
| Calvert City, KY | 2,544 | 36 | 28% |
| Wayne Heights, PA | 2,545 | 41 | 18% |
| Sheridan, IL | 2,543 | 1 | 98% |