| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 22°F | 36°F | 29°F | 2.2" |
| February | 22°F | 38°F | 29°F | 2.6" |
| March | 33°F | 51°F | 41°F | 4.9" |
| April | 43°F | 64°F | 53°F | 4.3" |
| May | 53°F | 74°F | 63°F | 5.0" |
| June | 61°F | 81°F | 71°F | 4.4" |
| July | 64°F | 82°F | 73°F | 8.1" |
| August | 62°F | 82°F | 72°F | 7.0" |
| September | 55°F | 76°F | 65°F | 5.2" |
| October | 44°F | 65°F | 54°F | 5.1" |
| November | 34°F | 53°F | 43°F | 4.0" |
| December | 27°F | 41°F | 34°F | 2.7" |
| Index | Williamsport | Ohio | National |
| Air quality index | 38 | 40 | 42 |
| Pollution index | 2,306,000 | 4,472,386 | 2,726,193 |
| Measurement | Total |
| Days measured | 355 |
| Days with good air quality | 332 |
| Days with moderate air quality | 23 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.710% |
| Benzene | 0.020% |
| Carbon Tetrachloride | 0.003% |
| Lead | 0.020% |
| Mercury | 0.070% |
| City | Population | Air Quality Index | National Avg. |
| New Holland, OH | 829 | 38 | 24.0% |
| Mount Sterling, OH | 2,023 | 38 | 24.0% |
| Pancoastburg, OH | 43 | 38 | 24.0% |
| Frankfort, OH | 1,314 | 38 | 24.0% |
| Darbyville, OH | 206 | 38 | 24.0% |
| Williamsport, OH | 962 | 38 | 24.0% |
| City | Population | Air Quality Index | National Avg. |
| Sully, IA | 962 | 39 | 22.0% |
| Anacoco, LA | 962 | 30 | 40.0% |
| Cotton Valley, LA | 962 | 39 | 22.0% |
| Alanson, MI | 962 | 36 | 28.0% |
| Clarkfield, MN | 962 | 32 | 36.0% |
| Williamsport, OH | 962 | 38 | 24.0% |
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