| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 17°F | 35°F | 25°F | 1.1" |
| February | 20°F | 38°F | 28°F | 1.5" |
| March | 33°F | 53°F | 41°F | 1.9" |
| April | 43°F | 65°F | 53°F | 3.7" |
| May | 53°F | 75°F | 64°F | 5.1" |
| June | 63°F | 84°F | 73°F | 5.5" |
| July | 66°F | 87°F | 76°F | 4.1" |
| August | 64°F | 84°F | 74°F | 3.3" |
| September | 56°F | 79°F | 67°F | 3.3" |
| October | 45°F | 68°F | 55°F | 3.0" |
| November | 33°F | 53°F | 42°F | 2.4" |
| December | 23°F | 39°F | 31°F | 1.9" |
| Index | La Harpe | Illinois | National |
| Air quality index | 29 | 41 | 42 |
| Pollution index | 802,114 | 3,148,694 | 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 | 0.001% |
| Benzene | 0.040% |
| Carbon Tetrachloride | 0.000% |
| Lead | 0.000% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Elvaston, IL | 151 | 29 | 42.0% |
| Colchester, IL | 1,347 | 29 | 42.0% |
| Raritan, IL | 123 | 29 | 42.0% |
| Ferris, IL | 164 | 29 | 42.0% |
| Gulf Port, IL | 21 | 29 | 42.0% |
| La Harpe, IL | 1,318 | 29 | 42.0% |
| City | Population | Air Quality Index | National Avg. |
| Julian, CA | 1,318 | 64 | 28.0% |
| Mulberry, IN | 1,319 | 42 | 16.0% |
| Coal Run Village, KY | 1,319 | 42 | 16.0% |
| Red Lake Falls, MN | 1,319 | 33 | 34.0% |
| Winthrop, MN | 1,317 | 46 | 8.0% |
| La Harpe, IL | 1,318 | 29 | 42.0% |
Here are the best places to live in Illinois
These are the 10 cheapest cities in Illinois
Most Dangerous Cities In The US
Check out the 10 safest cities in Illinois