| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 22°F | 36°F | 28°F | 5.9" |
| February | 16°F | 31°F | 23°F | 2.8" |
| March | 29°F | 49°F | 38°F | 2.2" |
| April | 38°F | 61°F | 49°F | 5.4" |
| May | 47°F | 74°F | 60°F | 3.5" |
| June | 60°F | 85°F | 72°F | 3.2" |
| July | 61°F | 85°F | 73°F | 7.1" |
| August | 62°F | 84°F | 73°F | 12.6" |
| September | 53°F | 80°F | 66°F | 4.9" |
| October | 47°F | 67°F | 56°F | 3.6" |
| November | 31°F | 52°F | 41°F | 6.4" |
| December | 21°F | 33°F | 27°F | 4.1" |
| Index | Defiance | Ohio | National |
| Air quality index | 39 | 40 | 42 |
| Pollution index | 3,123,630 | 4,472,386 | 2,726,193 |
| Measurement | Total |
| Days measured | 364 |
| Days with good air quality | 303 |
| Days with moderate air quality | 61 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.010% |
| Benzene | 0.040% |
| Carbon Tetrachloride | 0.010% |
| Lead | 0.040% |
| Mercury | 0.110% |
| City | Population | Air Quality Index | National Avg. |
| Miller City, OH | 142 | 39 | 22.0% |
| Ridgeville Corners, OH | 296 | 39 | 22.0% |
| Holgate, OH | 1,149 | 39 | 22.0% |
| Melrose, OH | 358 | 39 | 22.0% |
| New Bavaria, OH | 87 | 39 | 22.0% |
| Defiance, OH | 16,741 | 39 | 22.0% |
| City | Population | Air Quality Index | National Avg. |
| Seven Oaks, SC | 16,743 | 43 | 14.0% |
| Seagoville, TX | 16,726 | 51 | 2.0% |
| Clayton, MO | 16,763 | 54 | 8.0% |
| Bull Run, VA | 16,769 | 47 | 6.0% |
| Cohoes, NY | 16,708 | 37 | 26.0% |
| Defiance, OH | 16,741 | 39 | 22.0% |
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