| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 25°F | 40°F | 32°F | 8.4" |
| February | 17°F | 36°F | 27°F | 3.0" |
| March | 31°F | 51°F | 40°F | 5.7" |
| April | 38°F | 64°F | 51°F | 5.4" |
| May | 46°F | 75°F | 61°F | 4.4" |
| June | 59°F | 84°F | 72°F | 3.9" |
| July | 61°F | 85°F | 73°F | 5.2" |
| August | 63°F | 87°F | 74°F | 7.4" |
| September | 53°F | 81°F | 66°F | 2.6" |
| October | 45°F | 68°F | 56°F | 3.3" |
| November | 32°F | 55°F | 43°F | 6.2" |
| December | 23°F | 39°F | 31°F | 3.3" |
| Index | Hartford | Ohio | National |
| Air quality index | 41 | 40 | 42 |
| Pollution index | 3,612,840 | 4,472,386 | 2,726,193 |
| Measurement | Total |
| Days measured | 245 |
| Days with good air quality | 218 |
| Days with moderate air quality | 27 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.004% |
| Benzene | 0.040% |
| Carbon Tetrachloride | 0.010% |
| Lead | 0.030% |
| Mercury | 0.002% |
| City | Population | Air Quality Index | National Avg. |
| Mount Vernon, OH | 16,684 | 41 | 18.0% |
| Newark, OH | 49,951 | 41 | 18.0% |
| Ashley, OH | 1,672 | 41 | 18.0% |
| Sparta, OH | 179 | 41 | 18.0% |
| Utica, OH | 2,141 | 41 | 18.0% |
| Hartford, OH | 355 | 41 | 18.0% |
| City | Population | Air Quality Index | National Avg. |
| Rockford Bay, ID | 355 | 43 | 14.0% |
| Latham, IL | 355 | 44 | 12.0% |
| Ransom, IL | 355 | 0 | 100.0% |
| Gridley, KS | 355 | 22 | 56.0% |
| Spottsville, KY | 355 | 45 | 10.0% |
| Hartford, OH | 355 | 41 | 18.0% |
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