| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 23°F | 42°F | 32°F | 5.6" |
| February | 25°F | 45°F | 34°F | 3.8" |
| March | 37°F | 59°F | 47°F | 7.1" |
| April | 47°F | 70°F | 57°F | 10.2" |
| May | 56°F | 77°F | 66°F | 8.9" |
| June | 65°F | 87°F | 76°F | 9.2" |
| July | 68°F | 89°F | 78°F | 8.0" |
| August | 66°F | 88°F | 76°F | 7.8" |
| September | 58°F | 82°F | 69°F | 8.4" |
| October | 47°F | 70°F | 57°F | 8.6" |
| November | 36°F | 57°F | 46°F | 6.9" |
| December | 28°F | 45°F | 36°F | 8.2" |
| Index | Shiloh | Illinois | National |
| Air quality index | 54 | 41 | 50 |
| Pollution index | 6,055,640 | 3,347,295 | 5,066,862 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 134 |
| Days with moderate air quality | 221 |
| Days w/ poor A.Q. for sensitive groups | 8 |
| Days with unhealthy air quality | 2 |
| Pollutant | Total |
| Arsenic | 0.010% |
| Benzene | 0.070% |
| Carbon Tetrachloride | 0.040% |
| Lead | 0.100% |
| Mercury | 0.230% |
| City, State | Population | Air Quality Index | National Avg. |
| Glen Carbon, IL | 12,782 | 54 | 8% |
| St. Jacob, IL | 1,354 | 54 | 8% |
| Fairmont City, IL | 2,349 | 54 | 8% |
| Mascoutah, IL | 7,917 | 54 | 8% |
| Cahokia, IL | 14,574 | 54 | 8% |
| Shiloh, IL | 13,050 | 54 | 8% |
| City, State | Population | Air Quality Index | National Avg. |
| Lindsay, CA | 13,052 | 66 | 32% |
| Riverdale, IL | 13,047 | 55 | 10% |
| Oakland, NJ | 13,041 | 51 | 2% |
| Stoughton, WI | 13,041 | 39 | 22% |
| Hampton Bays, NY | 13,040 | 41 | 18% |
| Shiloh, IL | 13,050 | 54 | 8% |
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