| 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 | Delavan | Illinois | National |
| Air quality index | 41 | 41 | 42 |
| Pollution index | 672,031 | 3,148,694 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 285 |
| Days with moderate air quality | 78 |
| Days w/ poor A.Q. for sensitive groups | 2 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.001% |
| Benzene | 0.030% |
| Carbon Tetrachloride | 0.000% |
| Lead | 0.001% |
| Mercury | 0.020% |
| City | Population | Air Quality Index | National Avg. |
| Mason City, IL | 2,342 | 40 | 20.0% |
| New Holland, IL | 257 | 40 | 20.0% |
| Green Valley, IL | 716 | 41 | 18.0% |
| Mackinaw, IL | 1,970 | 41 | 18.0% |
| Kingston Mines, IL | 240 | 41 | 18.0% |
| Delavan, IL | 1,708 | 41 | 18.0% |
| City | Population | Air Quality Index | National Avg. |
| Mancelona, MI | 1,708 | 36 | 28.0% |
| Rawls Springs, MS | 1,708 | 35 | 30.0% |
| Garrison, ND | 1,708 | 36 | 28.0% |
| Santa Clara, NM | 1,708 | 37 | 26.0% |
| Langham, SK | 1,708 | n/a | |
| Delavan, IL | 1,708 | 41 | 18.0% |
Here are the best places to live in Illinois
These are the 10 cheapest cities in Illinois
See the best places to live in Delavan
Check out the 10 safest cities in Illinois