| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 17°F | 34°F | 25°F | 0.7" |
| February | 18°F | 36°F | 26°F | 2.1" |
| March | 33°F | 53°F | 41°F | 4.1" |
| April | 43°F | 66°F | 53°F | 4.8" |
| May | 53°F | 75°F | 63°F | 6.2" |
| June | 63°F | 84°F | 73°F | 5.9" |
| July | 65°F | 86°F | 75°F | 5.6" |
| August | 63°F | 84°F | 73°F | 2.0" |
| September | 55°F | 79°F | 65°F | 4.1" |
| October | 44°F | 66°F | 54°F | 6.1" |
| November | 33°F | 51°F | 41°F | 3.3" |
| December | 22°F | 38°F | 30°F | 3.1" |
| Index | Hillsboro | Iowa | National |
| Air quality index | 29 | 39 | 42 |
| Pollution index | 464,333 | 1,154,535 | 2,726,193 |
| Measurement | Total |
| Days measured | 120 |
| Days with good air quality | 101 |
| Days with moderate air quality | 19 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.000% |
| Benzene | 0.010% |
| Carbon Tetrachloride | 0.001% |
| Lead | 0.320% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Birmingham, IA | 512 | 29 | 42.0% |
| Franklin, IA | 175 | 29 | 42.0% |
| Salem, IA | 492 | 29 | 42.0% |
| Lockridge, IA | 764 | 29 | 42.0% |
| Bonaparte, IA | 461 | 29 | 42.0% |
| Hillsboro, IA | 187 | 29 | 42.0% |
| City | Population | Air Quality Index | National Avg. |
| Fox, AK | 187 | 38 | 24.0% |
| Morristown, AZ | 187 | 74 | 48.0% |
| Coffee Creek, CA | 187 | 42 | 16.0% |
| Markleeville, CA | 187 | 13 | 74.0% |
| Henlopen Acres, DE | 187 | 36 | 28.0% |
| Hillsboro, IA | 187 | 29 | 42.0% |
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