| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 22°F | 38°F | 30°F | 3.0" |
| February | 22°F | 40°F | 31°F | 2.8" |
| March | 33°F | 53°F | 42°F | 4.5" |
| April | 43°F | 66°F | 54°F | 4.5" |
| May | 52°F | 75°F | 63°F | 4.1" |
| June | 61°F | 83°F | 72°F | 4.9" |
| July | 63°F | 85°F | 73°F | 4.0" |
| August | 61°F | 84°F | 72°F | 3.3" |
| September | 55°F | 79°F | 66°F | 3.3" |
| October | 44°F | 67°F | 55°F | 4.1" |
| November | 33°F | 55°F | 43°F | 3.3" |
| December | 27°F | 43°F | 34°F | 3.9" |
| Index | Wilmington | Ohio | National |
| Air quality index | 43 | 40 | 42 |
| Pollution index | 735,656 | 4,472,386 | 2,726,193 |
| Measurement | Total |
| Days measured | 244 |
| Days with good air quality | 203 |
| Days with moderate air quality | 41 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.010% |
| Benzene | 0.030% |
| Carbon Tetrachloride | 0.000% |
| Lead | 0.003% |
| Mercury | 0.150% |
| City | Population | Air Quality Index | National Avg. |
| Octa, OH | 51 | 38 | 24.0% |
| Leesburg, OH | 1,449 | 38 | 24.0% |
| Jeffersonville, OH | 1,081 | 38 | 24.0% |
| Milledgeville, OH | 116 | 38 | 24.0% |
| Midland, OH | 371 | 43 | 14.0% |
| Wilmington, OH | 12,444 | 43 | 14.0% |
| City | Population | Air Quality Index | National Avg. |
| Cheney, WA | 12,455 | 43 | 14.0% |
| Fort Atkinson, WI | 12,455 | 37 | 26.0% |
| West Monroe, LA | 12,431 | 34 | 32.0% |
| Troy, MO | 12,457 | 54 | 8.0% |
| Palos Heights, IL | 12,460 | 55 | 10.0% |
| Wilmington, OH | 12,444 | 43 | 14.0% |
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