| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 24°F | 41°F | 31°F | 5.3" |
| February | 26°F | 43°F | 33°F | 3.7" |
| March | 38°F | 57°F | 46°F | 4.5" |
| April | 47°F | 69°F | 57°F | 8.3" |
| May | 56°F | 77°F | 66°F | 6.2" |
| June | 65°F | 86°F | 75°F | 8.8" |
| July | 67°F | 88°F | 77°F | 7.5" |
| August | 65°F | 87°F | 75°F | 7.1" |
| September | 58°F | 81°F | 68°F | 8.8" |
| October | 47°F | 70°F | 57°F | 6.4" |
| November | 36°F | 57°F | 45°F | 7.2" |
| December | 29°F | 45°F | 36°F | 5.8" |
| Index | Olney | Illinois | National |
| Air quality index | 36 | 41 | 42 |
| Pollution index | 500,004 | 3,148,694 | 2,726,193 |
| Measurement | Total |
| Days measured | 359 |
| Days with good air quality | 328 |
| Days with moderate air quality | 31 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| 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. |
| West Salem, IL | 872 | 36 | 28.0% |
| Calhoun, IL | 149 | 36 | 28.0% |
| Claremont, IL | 218 | 36 | 28.0% |
| Parkersburg, IL | 223 | 36 | 28.0% |
| Sumner, IL | 2,916 | 36 | 28.0% |
| Olney, IL | 8,872 | 36 | 28.0% |
| City | Population | Air Quality Index | National Avg. |
| Toppenish, WA | 8,872 | 38 | 24.0% |
| Farmingdale, NY | 8,869 | 51 | 2.0% |
| South Amboy, NJ | 8,868 | 51 | 2.0% |
| Newark, NY | 8,868 | 37 | 26.0% |
| New Windsor, NY | 8,866 | 36 | 28.0% |
| Olney, IL | 8,872 | 36 | 28.0% |
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