| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 22°F | 36°F | 29°F | 6.9" |
| February | 19°F | 34°F | 26°F | 3.4" |
| March | 33°F | 54°F | 42°F | 3.3" |
| April | 41°F | 65°F | 52°F | 5.8" |
| May | 52°F | 78°F | 65°F | 3.4" |
| June | 63°F | 85°F | 74°F | 6.1" |
| July | 63°F | 83°F | 73°F | 5.8" |
| August | 65°F | 86°F | 75°F | 5.4" |
| September | 57°F | 83°F | 69°F | 7.0" |
| October | 46°F | 69°F | 57°F | 5.6" |
| November | 33°F | 53°F | 42°F | 7.3" |
| December | 21°F | 35°F | 27°F | 3.7" |
| Index | St. Joseph | Illinois | National |
| Air quality index | 42 | 41 | 42 |
| Pollution index | 9,793,540 | 3,148,694 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 281 |
| Days with moderate air quality | 84 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.010% |
| Benzene | 0.070% |
| Carbon Tetrachloride | 0.010% |
| Lead | 0.001% |
| Mercury | 0.040% |
| City | Population | Air Quality Index | National Avg. |
| Gifford, IL | 920 | 42 | 16.0% |
| Thomasboro, IL | 1,036 | 42 | 16.0% |
| Broadlands, IL | 340 | 42 | 16.0% |
| Fithian, IL | 536 | 42 | 16.0% |
| Urbana, IL | 42,461 | 42 | 16.0% |
| St. Joseph, IL | 4,053 | 42 | 16.0% |
| City | Population | Air Quality Index | National Avg. |
| Cannon Falls, MN | 4,053 | 37 | 26.0% |
| St. James, MO | 4,053 | 39 | 22.0% |
| Northern Lights County, AB | 4,053 | n/a | |
| Mount Olive, AL | 4,052 | 53 | 6.0% |
| Singac, NJ | 4,054 | 51 | 2.0% |
| St. Joseph, IL | 4,053 | 42 | 16.0% |
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