| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 25°F | 42°F | 33°F | 4.6" |
| February | 27°F | 45°F | 35°F | 2.4" |
| March | 39°F | 58°F | 48°F | 3.7" |
| April | 48°F | 69°F | 58°F | 6.6" |
| May | 57°F | 77°F | 66°F | 10.0" |
| June | 66°F | 86°F | 76°F | 8.8" |
| July | 69°F | 88°F | 78°F | 6.8" |
| August | 67°F | 87°F | 76°F | 10.7" |
| September | 59°F | 81°F | 69°F | 7.4" |
| October | 48°F | 70°F | 58°F | 9.0" |
| November | 38°F | 57°F | 47°F | 6.5" |
| December | 30°F | 45°F | 37°F | 7.7" |
| Index | Percy | Illinois | National |
| Air quality index | 43 | 41 | 42 |
| Pollution index | 569,178 | 3,148,694 | 2,726,193 |
| Measurement | Total |
| Days measured | 344 |
| Days with good air quality | 269 |
| Days with moderate air quality | 74 |
| Days w/ poor A.Q. for sensitive groups | 1 |
| 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. |
| Campbell Hill, IL | 292 | 43 | 14.0% |
| Tilden, IL | 961 | 43 | 14.0% |
| Rockwood, IL | 25 | 43 | 14.0% |
| Steeleville, IL | 1,870 | 43 | 14.0% |
| Cutler, IL | 429 | 43 | 14.0% |
| Percy, IL | 1,110 | 43 | 14.0% |
| City | Population | Air Quality Index | National Avg. |
| Hotevilla-Bacavi, AZ | 1,110 | 45 | 10.0% |
| Black Diamond, FL | 1,110 | 30 | 40.0% |
| Johnson City, KS | 1,110 | 15 | 70.0% |
| Algonquin, MD | 1,110 | 41 | 18.0% |
| Grant, MI | 1,110 | 38 | 24.0% |
| Percy, IL | 1,110 | 43 | 14.0% |
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