| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 18°F | 34°F | 25°F | 3.2" |
| February | 19°F | 36°F | 27°F | 2.6" |
| March | 32°F | 51°F | 40°F | 3.2" |
| April | 41°F | 64°F | 51°F | 5.2" |
| May | 51°F | 74°F | 62°F | 5.3" |
| June | 61°F | 83°F | 71°F | 9.7" |
| July | 64°F | 86°F | 74°F | 5.3" |
| August | 62°F | 84°F | 73°F | 9.8" |
| September | 55°F | 79°F | 66°F | 6.1" |
| October | 44°F | 65°F | 54°F | 7.0" |
| November | 34°F | 52°F | 42°F | 3.8" |
| December | 24°F | 38°F | 31°F | 3.7" |
| Index | Irwin | Illinois | National |
| Air quality index | 0 | 41 | 42 |
| Pollution index | 3,962,360 | 3,148,694 | 2,726,193 |
| Measurement | Total |
| Days measured | 335 |
| Days with good air quality | 334 |
| Days with moderate air quality | 1 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.002% |
| Benzene | 0.070% |
| Carbon Tetrachloride | 0.020% |
| Lead | 0.300% |
| Mercury | 0.110% |
| City | Population | Air Quality Index | National Avg. |
| Bonfield, IL | 586 | 0 | 100.0% |
| East Brooklyn, IL | 57 | 0 | 100.0% |
| Limestone, IL | 1,536 | 0 | 100.0% |
| Cabery, IL | 260 | 0 | 100.0% |
| Cullom, IL | 501 | 0 | 100.0% |
| Irwin, IL | 39 | 0 | 100.0% |
| City | Population | Air Quality Index | National Avg. |
| Stony River, AK | 39 | 31 | 38.0% |
| Sunrise, AK | 39 | 31 | 38.0% |
| Tibbie, AL | 39 | 42 | 16.0% |
| Haigler Creek, AZ | 39 | 60 | 20.0% |
| Edgewood, CA | 39 | 42 | 16.0% |
| Irwin, IL | 39 | 0 | 100.0% |
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