| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 20°F | 37°F | 28°F | 2.6" |
| February | 21°F | 39°F | 29°F | 3.2" |
| March | 34°F | 55°F | 43°F | 4.1" |
| April | 44°F | 67°F | 55°F | 6.7" |
| May | 54°F | 76°F | 65°F | 4.6" |
| June | 63°F | 85°F | 74°F | 8.5" |
| July | 66°F | 87°F | 76°F | 11.2" |
| August | 64°F | 86°F | 74°F | 8.1" |
| September | 56°F | 80°F | 67°F | 11.5" |
| October | 46°F | 68°F | 56°F | 6.3" |
| November | 34°F | 54°F | 43°F | 5.1" |
| December | 25°F | 40°F | 32°F | 5.3" |
| Index | Latham | Illinois | National |
| Air quality index | 44 | 41 | 42 |
| Pollution index | 1,277,890 | 3,148,694 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 255 |
| Days with moderate air quality | 110 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.010% |
| Benzene | 0.050% |
| Carbon Tetrachloride | 0.000% |
| Lead | 0.010% |
| Mercury | 0.002% |
| City | Population | Air Quality Index | National Avg. |
| Mechanicsburg, IL | 918 | 40 | 20.0% |
| Broadwell, IL | 188 | 40 | 20.0% |
| Lincoln, IL | 13,742 | 40 | 20.0% |
| Cornland, IL | 71 | 40 | 20.0% |
| Buffalo, IL | 345 | 40 | 20.0% |
| Latham, IL | 355 | 44 | 12.0% |
| City | Population | Air Quality Index | National Avg. |
| Rockford Bay, ID | 355 | 43 | 14.0% |
| Ransom, IL | 355 | 0 | 100.0% |
| Gridley, KS | 355 | 22 | 56.0% |
| Spottsville, KY | 355 | 45 | 10.0% |
| Branch, LA | 355 | 41 | 18.0% |
| Latham, IL | 355 | 44 | 12.0% |
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