| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 17°F | 37°F | 26°F | 2.3" |
| February | 18°F | 39°F | 28°F | 2.1" |
| March | 31°F | 54°F | 42°F | 3.1" |
| April | 41°F | 67°F | 54°F | 4.7" |
| May | 51°F | 77°F | 64°F | 4.4" |
| June | 62°F | 85°F | 73°F | 5.4" |
| July | 65°F | 88°F | 76°F | 3.4" |
| August | 64°F | 86°F | 74°F | 3.5" |
| September | 56°F | 81°F | 68°F | 4.1" |
| October | 44°F | 68°F | 55°F | 3.4" |
| November | 33°F | 55°F | 43°F | 2.9" |
| December | 22°F | 39°F | 30°F | 2.7" |
| Index | Farmington | Illinois | National |
| Air quality index | 41 | 41 | 42 |
| Pollution index | 1,709,230 | 3,148,694 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 285 |
| Days with moderate air quality | 78 |
| Days w/ poor A.Q. for sensitive groups | 2 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.001% |
| Benzene | 0.050% |
| Carbon Tetrachloride | 0.040% |
| Lead | 0.001% |
| Mercury | 0.001% |
| City | Population | Air Quality Index | National Avg. |
| Cuba, IL | 1,066 | 41 | 18.0% |
| London Mills, IL | 326 | 41 | 18.0% |
| Elmwood, IL | 2,492 | 41 | 18.0% |
| Lake Camelot, IL | 1,631 | 41 | 18.0% |
| Yates City, IL | 821 | 41 | 18.0% |
| Farmington, IL | 1,939 | 41 | 18.0% |
| City | Population | Air Quality Index | National Avg. |
| Chuluota, FL | 1,939 | 39 | 22.0% |
| Fennville, MI | 1,939 | 38 | 24.0% |
| Blooming Prairie, MN | 1,939 | 36 | 28.0% |
| Winchester, NH | 1,939 | 34 | 32.0% |
| Homerville, GA | 1,938 | 26 | 48.0% |
| Farmington, IL | 1,939 | 41 | 18.0% |
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