| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 14°F | 30°F | 22°F | 3.8" |
| February | 14°F | 32°F | 23°F | 3.4" |
| March | 29°F | 48°F | 37°F | 4.3" |
| April | 39°F | 62°F | 50°F | 4.5" |
| May | 50°F | 74°F | 61°F | 5.4" |
| June | 59°F | 81°F | 70°F | 6.7" |
| July | 61°F | 82°F | 71°F | 6.0" |
| August | 59°F | 81°F | 69°F | 6.4" |
| September | 51°F | 76°F | 63°F | 3.8" |
| October | 41°F | 63°F | 51°F | 7.1" |
| November | 29°F | 48°F | 38°F | 3.9" |
| December | 19°F | 34°F | 26°F | 3.6" |
| Index | Oregon | Illinois | National |
| Air quality index | 42 | 41 | 42 |
| Pollution index | 1,721,090 | 3,148,694 | 2,726,193 |
| Measurement | Total |
| Days measured | 341 |
| Days with good air quality | 240 |
| Days with moderate air quality | 100 |
| Days w/ poor A.Q. for sensitive groups | 1 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.001% |
| Benzene | 0.020% |
| Carbon Tetrachloride | 0.001% |
| Lead | 0.002% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Hillcrest, IL | 1,672 | 42 | 16.0% |
| Forreston, IL | 1,392 | 42 | 16.0% |
| New Milford, IL | 1,356 | 42 | 16.0% |
| Grand Detour, IL | 351 | 42 | 16.0% |
| Adeline, IL | 99 | 42 | 16.0% |
| Oregon, IL | 3,747 | 42 | 16.0% |
| City | Population | Air Quality Index | National Avg. |
| Bishop, CA | 3,747 | 47 | 6.0% |
| Norwood Young America, MN | 3,746 | 46 | 8.0% |
| Fordyce, AR | 3,748 | 32 | 36.0% |
| McGehee, AR | 3,748 | 43 | 14.0% |
| St. Charles, MN | 3,749 | 15 | 70.0% |
| Oregon, IL | 3,747 | 42 | 16.0% |
Here are the best places to live in Illinois
Check out the 10 safest cities in Illinois
These are the 10 most affordable cities in Illinois
10 best cities to buy a new house in Illinois