| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 20°F | 38°F | 29°F | 2.1" |
| February | 22°F | 41°F | 31°F | 1.9" |
| March | 34°F | 56°F | 44°F | 2.9" |
| April | 44°F | 68°F | 56°F | 4.3" |
| May | 54°F | 77°F | 65°F | 4.5" |
| June | 64°F | 86°F | 74°F | 5.5" |
| July | 66°F | 88°F | 77°F | 4.3" |
| August | 64°F | 86°F | 75°F | 3.2" |
| September | 57°F | 81°F | 68°F | 3.7" |
| October | 46°F | 69°F | 56°F | 3.7" |
| November | 36°F | 55°F | 45°F | 2.5" |
| December | 26°F | 41°F | 33°F | 2.8" |
| Index | Williamsville | Illinois | National |
| Air quality index | 40 | 41 | 42 |
| Pollution index | 1,277,890 | 3,148,694 | 2,726,193 |
| Measurement | Total |
| Days measured | 360 |
| Days with good air quality | 287 |
| Days with moderate air quality | 73 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.010% |
| Benzene | 0.050% |
| Carbon Tetrachloride | 0.000% |
| Lead | 0.010% |
| Mercury | 0.002% |
| City | Population | Air Quality Index | National Avg. |
| Curran, IL | 212 | 40 | 20.0% |
| Mechanicsburg, IL | 918 | 40 | 20.0% |
| Lincoln, IL | 13,742 | 40 | 20.0% |
| Riverton, IL | 3,464 | 40 | 20.0% |
| Broadwell, IL | 188 | 40 | 20.0% |
| Williamsville, IL | 1,468 | 40 | 20.0% |
| City | Population | Air Quality Index | National Avg. |
| Bunker Hill, IL | 1,468 | 54 | 8.0% |
| Clarkson, KY | 1,468 | 39 | 22.0% |
| Leavittsburg, OH | 1,468 | 42 | 16.0% |
| Stratford, OK | 1,468 | 36 | 28.0% |
| University of Pittsburgh Johnstown, PA | 1,468 | 39 | 22.0% |
| Williamsville, IL | 1,468 | 40 | 20.0% |
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