| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 29°F | 46°F | 37°F | 4.5" |
| February | 31°F | 49°F | 39°F | 3.7" |
| March | 41°F | 61°F | 50°F | 7.8" |
| April | 51°F | 72°F | 61°F | 7.9" |
| May | 60°F | 80°F | 69°F | 6.9" |
| June | 69°F | 90°F | 79°F | 6.4" |
| July | 70°F | 90°F | 79°F | 5.7" |
| August | 68°F | 89°F | 77°F | 4.3" |
| September | 60°F | 83°F | 70°F | 2.8" |
| October | 49°F | 73°F | 60°F | 4.4" |
| November | 39°F | 60°F | 49°F | 8.5" |
| December | 33°F | 49°F | 40°F | 8.2" |
| Index | Ullin | Illinois | National |
| Air quality index | 44 | 41 | 42 |
| Pollution index | 1,566,340 | 3,148,694 | 2,726,193 |
| Measurement | Total |
| Days measured | 364 |
| Days with good air quality | 261 |
| Days with moderate air quality | 103 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.001% |
| Benzene | 0.010% |
| Carbon Tetrachloride | 0.001% |
| Lead | 0.000% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Jonesboro, IL | 1,772 | 44 | 12.0% |
| Olive Branch, IL | 610 | 44 | 12.0% |
| Belknap, IL | 142 | 44 | 12.0% |
| Mound City, IL | 777 | 44 | 12.0% |
| La Center, KY | 700 | 44 | 12.0% |
| Ullin, IL | 579 | 44 | 12.0% |
| City | Population | Air Quality Index | National Avg. |
| Jacumba, CA | 579 | 58 | 16.0% |
| East Galesburg, IL | 579 | 41 | 18.0% |
| LeRoy, KS | 579 | 22 | 56.0% |
| Laddonia, MO | 579 | 38 | 24.0% |
| Pryor, MT | 579 | 21 | 58.0% |
| Ullin, IL | 579 | 44 | 12.0% |
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