| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 23°F | 42°F | 32°F | 5.6" |
| February | 25°F | 45°F | 34°F | 3.8" |
| March | 37°F | 59°F | 47°F | 7.1" |
| April | 47°F | 70°F | 57°F | 10.2" |
| May | 56°F | 77°F | 66°F | 8.9" |
| June | 65°F | 87°F | 76°F | 9.2" |
| July | 68°F | 89°F | 78°F | 8.0" |
| August | 66°F | 88°F | 76°F | 7.8" |
| September | 58°F | 82°F | 69°F | 8.4" |
| October | 47°F | 70°F | 57°F | 8.6" |
| November | 36°F | 57°F | 46°F | 6.9" |
| December | 28°F | 45°F | 36°F | 8.2" |
| Index | Pierron | Illinois | National |
| Air quality index | 54 | 41 | 42 |
| Pollution index | 647,280 | 3,148,694 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 134 |
| Days with moderate air quality | 221 |
| Days w/ poor A.Q. for sensitive groups | 8 |
| Days with unhealthy air quality | 2 |
| Pollutant | Total |
| Arsenic | 0.001% |
| Benzene | 0.020% |
| Carbon Tetrachloride | 0.000% |
| Lead | 0.000% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Smithboro, IL | 215 | 40 | 20.0% |
| Carlyle, IL | 3,595 | 43 | 14.0% |
| Beckemeyer, IL | 1,054 | 43 | 14.0% |
| Breese, IL | 4,160 | 43 | 14.0% |
| Greenville, IL | 6,725 | 43 | 14.0% |
| Pierron, IL | 393 | 54 | 8.0% |
| City | Population | Air Quality Index | National Avg. |
| Carbon, IN | 393 | 45 | 10.0% |
| Clifton, KS | 393 | 32 | 36.0% |
| Vicco, KY | 393 | 39 | 22.0% |
| Downing, MO | 393 | 29 | 42.0% |
| Gowen, OK | 393 | 43 | 14.0% |
| Pierron, IL | 393 | 54 | 8.0% |
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