| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 20°F | 38°F | 29°F | 2.1" |
| February | 22°F | 41°F | 31°F | 1.9" |
| March | 34°F | 56°F | 44°F | 2.9" |
| April | 44°F | 68°F | 56°F | 4.3" |
| May | 54°F | 77°F | 65°F | 4.5" |
| June | 64°F | 86°F | 74°F | 5.5" |
| July | 66°F | 88°F | 77°F | 4.3" |
| August | 64°F | 86°F | 75°F | 3.2" |
| September | 57°F | 81°F | 68°F | 3.7" |
| October | 46°F | 69°F | 56°F | 3.7" |
| November | 36°F | 55°F | 45°F | 2.5" |
| December | 26°F | 41°F | 33°F | 2.8" |
| Index | Thayer | Illinois | National |
| Air quality index | 40 | 41 | 42 |
| Pollution index | 1,150,670 | 3,148,694 | 2,726,193 |
| Measurement | Total |
| Days measured | 360 |
| Days with good air quality | 287 |
| Days with moderate air quality | 73 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.001% |
| Benzene | 0.030% |
| Carbon Tetrachloride | 0.000% |
| Lead | 0.000% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Palmyra, IL | 647 | 40 | 20.0% |
| Divernon, IL | 1,194 | 40 | 20.0% |
| Rochester, IL | 3,778 | 40 | 20.0% |
| Modesto, IL | 222 | 40 | 20.0% |
| Standard City, IL | 219 | 40 | 20.0% |
| Thayer, IL | 622 | 40 | 20.0% |
| City | Population | Air Quality Index | National Avg. |
| Cedarville, IL | 622 | 42 | 16.0% |
| Cloverdale, MS | 622 | 30 | 40.0% |
| Barnhill, OH | 622 | 46 | 8.0% |
| Furman, SC | 622 | 29 | 42.0% |
| Wattsville, VA | 622 | 36 | 28.0% |
| Thayer, IL | 622 | 40 | 20.0% |
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