| 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. |
| Continental, OH | 1,408 | 39 | 22.0% |
| Bryan, OH | 8,243 | 39 | 22.0% |
| Miller City, OH | 142 | 39 | 22.0% |
| Ridgeville Corners, OH | 296 | 39 | 22.0% |
| Holgate, OH | 1,149 | 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% |
Here are the best places to live in Ohio
10 Best cities in Ohio for employment
Top 10 cities in Ohio with the best education system
10 best cities to buy a new house in Ohio