| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 14°F | 30°F | 22°F | 2.9" |
| February | 15°F | 31°F | 23°F | 2.3" |
| March | 29°F | 47°F | 37°F | 3.6" |
| April | 38°F | 61°F | 48°F | 5.4" |
| May | 49°F | 72°F | 60°F | 5.5" |
| June | 58°F | 80°F | 69°F | 6.3" |
| July | 62°F | 82°F | 72°F | 5.8" |
| August | 60°F | 81°F | 70°F | 7.3" |
| September | 52°F | 75°F | 63°F | 4.7" |
| October | 42°F | 62°F | 51°F | 5.8" |
| November | 30°F | 48°F | 39°F | 4.0" |
| December | 19°F | 33°F | 26°F | 3.4" |
| Index | Freeport | Illinois | National |
| Air quality index | 42 | 41 | 42 |
| Pollution index | 1,767,980 | 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 | 0.040% |
| Carbon Tetrachloride | 0.010% |
| Lead | 0.001% |
| Mercury | 0.003% |
| City | Population | Air Quality Index | National Avg. |
| Winslow, IL | 324 | 29 | 42.0% |
| Lake Summerset, IL | 1,958 | 42 | 16.0% |
| Leaf River, IL | 510 | 42 | 16.0% |
| Pecatonica, IL | 1,957 | 42 | 16.0% |
| Lena, IL | 2,780 | 42 | 16.0% |
| Freeport, IL | 23,930 | 42 | 16.0% |
| City | Population | Air Quality Index | National Avg. |
| Kalispell, MT | 23,935 | 37 | 26.0% |
| Port St. John, FL | 23,940 | 39 | 22.0% |
| Ponca City, OK | 23,940 | 40 | 20.0% |
| Saint-Lin--Laurentides, QC | 23,910 | n/a | |
| South Plainfield, NJ | 23,961 | 51 | 2.0% |
| Freeport, IL | 23,930 | 42 | 16.0% |
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