| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 19°F | 36°F | 27°F | 2.6" |
| February | 20°F | 39°F | 29°F | 2.0" |
| March | 32°F | 53°F | 42°F | 2.7" |
| April | 42°F | 66°F | 53°F | 4.3" |
| May | 51°F | 75°F | 63°F | 4.4" |
| June | 61°F | 84°F | 72°F | 5.8" |
| July | 64°F | 85°F | 74°F | 4.8" |
| August | 62°F | 85°F | 73°F | 3.6" |
| September | 55°F | 79°F | 66°F | 3.2" |
| October | 44°F | 67°F | 55°F | 3.3" |
| November | 33°F | 53°F | 43°F | 3.1" |
| December | 24°F | 40°F | 31°F | 3.1" |
| Index | Monticello | Indiana | National |
| Air quality index | 42 | 56 | 42 |
| Pollution index | 2,150,900 | 2,719,453 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 276 |
| Days with moderate air quality | 89 |
| 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 | 0.004% |
| Lead | 0.650% |
| Mercury | 1.040% |
| City | Population | Air Quality Index | National Avg. |
| Royal Center, IN | 890 | 37 | 26.0% |
| Delphi, IN | 2,979 | 42 | 16.0% |
| Reynolds, IN | 506 | 42 | 16.0% |
| Monon, IN | 1,650 | 42 | 16.0% |
| Brookston, IN | 1,398 | 42 | 16.0% |
| Monticello, IN | 5,255 | 42 | 16.0% |
| City | Population | Air Quality Index | National Avg. |
| Greenacres, CA | 5,255 | 67 | 34.0% |
| Briar, TX | 5,255 | 33 | 34.0% |
| Williamston, NC | 5,251 | 0 | 100.0% |
| Bowling Green, MO | 5,259 | 41 | 18.0% |
| Kings Point, NY | 5,250 | 51 | 2.0% |
| Monticello, IN | 5,255 | 42 | 16.0% |
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