| 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 | Hartsburg | Illinois | National |
| Air quality index | 44 | 41 | 42 |
| Pollution index | 1,277,890 | 3,148,694 | 2,726,193 |
| Measurement | Total |
| Days measured | 364 |
| Days with good air quality | 256 |
| Days with moderate air quality | 108 |
| 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. |
| Middletown, IL | 212 | 40 | 20.0% |
| New Holland, IL | 257 | 40 | 20.0% |
| Lincoln, IL | 13,742 | 40 | 20.0% |
| Mason City, IL | 2,342 | 40 | 20.0% |
| Broadwell, IL | 188 | 40 | 20.0% |
| Hartsburg, IL | 386 | 44 | 12.0% |
| City | Population | Air Quality Index | National Avg. |
| Newington, GA | 386 | 39 | 22.0% |
| Addieville, IL | 386 | 43 | 14.0% |
| Carbon Hill, IL | 386 | 0 | 100.0% |
| Clear Lake, IL | 386 | 40 | 20.0% |
| Longton, KS | 386 | 40 | 20.0% |
| Hartsburg, IL | 386 | 44 | 12.0% |
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