| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 20°F | 36°F | 27°F | 5.6" |
| February | 20°F | 37°F | 28°F | 3.2" |
| March | 33°F | 53°F | 42°F | 4.2" |
| April | 44°F | 66°F | 54°F | 7.2" |
| May | 54°F | 75°F | 64°F | 7.5" |
| June | 63°F | 84°F | 73°F | 7.8" |
| July | 64°F | 85°F | 74°F | 7.8" |
| August | 62°F | 84°F | 73°F | 10.6" |
| September | 56°F | 79°F | 66°F | 7.9" |
| October | 45°F | 67°F | 55°F | 7.0" |
| November | 34°F | 53°F | 43°F | 6.5" |
| December | 26°F | 40°F | 32°F | 5.0" |
| Index | Fairmount | Illinois | National |
| Air quality index | 42 | 41 | 42 |
| Pollution index | 9,793,540 | 3,148,694 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 281 |
| Days with moderate air quality | 84 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.010% |
| Benzene | 0.070% |
| Carbon Tetrachloride | 0.010% |
| Lead | 0.001% |
| Mercury | 0.040% |
| City | Population | Air Quality Index | National Avg. |
| Belgium, IL | 383 | 42 | 16.0% |
| Broadlands, IL | 340 | 42 | 16.0% |
| Fithian, IL | 536 | 42 | 16.0% |
| St. Joseph, IL | 4,053 | 42 | 16.0% |
| Homer, IL | 1,320 | 42 | 16.0% |
| Fairmount, IL | 540 | 42 | 16.0% |
| City | Population | Air Quality Index | National Avg. |
| Kenwood, CA | 540 | 34 | 32.0% |
| Industry, IL | 540 | 29 | 42.0% |
| Tallula, IL | 540 | 40 | 20.0% |
| South Mansfield, LA | 540 | 39 | 22.0% |
| North Adams, MI | 540 | 39 | 22.0% |
| Fairmount, IL | 540 | 42 | 16.0% |
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