| 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 | Iroquois | Illinois | National |
| Air quality index | 42 | 41 | 42 |
| Pollution index | 2,020,430 | 3,148,694 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 276 |
| Days with moderate air quality | 89 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.002% |
| Benzene | 0.090% |
| Carbon Tetrachloride | 0.000% |
| Lead | 0.000% |
| Mercury | 0.001% |
| City | Population | Air Quality Index | National Avg. |
| Sammons Point, IL | 207 | 0 | 100.0% |
| Milford, IL | 1,230 | 42 | 16.0% |
| Martinton, IL | 346 | 42 | 16.0% |
| Watseka, IL | 4,956 | 42 | 16.0% |
| Brook, IN | 1,000 | 42 | 16.0% |
| Iroquois, IL | 287 | 42 | 16.0% |
| City | Population | Air Quality Index | National Avg. |
| Bowles, CA | 287 | 60 | 20.0% |
| Mentor, KY | 287 | 54 | 8.0% |
| Parsonsburg, MD | 287 | 36 | 28.0% |
| Pecktonville, MD | 287 | 40 | 20.0% |
| Leonard, ND | 287 | 33 | 34.0% |
| Iroquois, IL | 287 | 42 | 16.0% |
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