| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 22°F | 41°F | 31°F | 2.7" |
| February | 22°F | 43°F | 32°F | 2.6" |
| March | 33°F | 57°F | 44°F | 4.4" |
| April | 43°F | 69°F | 55°F | 5.1" |
| May | 52°F | 77°F | 64°F | 4.4" |
| June | 61°F | 85°F | 73°F | 4.7" |
| July | 64°F | 87°F | 75°F | 3.7" |
| August | 62°F | 87°F | 74°F | 2.8" |
| September | 55°F | 81°F | 67°F | 3.8" |
| October | 43°F | 69°F | 55°F | 3.8" |
| November | 32°F | 57°F | 43°F | 3.1" |
| December | 27°F | 46°F | 36°F | 4.1" |
| Index | Millville | Ohio | National |
| Air quality index | 54 | 40 | 42 |
| Pollution index | 7,300,490 | 4,472,386 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 139 |
| Days with moderate air quality | 206 |
| Days w/ poor A.Q. for sensitive groups | 20 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.520% |
| Benzene | 0.070% |
| Carbon Tetrachloride | 0.040% |
| Lead | 0.240% |
| Mercury | 0.050% |
| City | Population | Air Quality Index | National Avg. |
| Darrtown, OH | 550 | 6 | 88.0% |
| Somerville, OH | 304 | 6 | 88.0% |
| West College Corner, IN | 505 | 6 | 88.0% |
| Oxford, OH | 23,192 | 6 | 88.0% |
| College Corner, OH | 276 | 6 | 88.0% |
| Millville, OH | 644 | 54 | 8.0% |
| City | Population | Air Quality Index | National Avg. |
| Kingston, GA | 644 | 44 | 12.0% |
| Halaula, HI | 644 | 16 | 68.0% |
| Albion, IA | 644 | 37 | 26.0% |
| Farmington, IA | 644 | 29 | 42.0% |
| Mount Auburn, IL | 644 | 44 | 12.0% |
| Millville, OH | 644 | 54 | 8.0% |
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