| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 18°F | 34°F | 26°F | 3.3" |
| February | 19°F | 35°F | 26°F | 3.0" |
| March | 32°F | 51°F | 40°F | 4.3" |
| April | 42°F | 64°F | 52°F | 7.2" |
| May | 53°F | 75°F | 63°F | 8.0" |
| June | 62°F | 83°F | 72°F | 7.5" |
| July | 66°F | 85°F | 75°F | 7.1" |
| August | 64°F | 83°F | 73°F | 8.2" |
| September | 56°F | 78°F | 66°F | 6.3" |
| October | 45°F | 65°F | 54°F | 6.6" |
| November | 34°F | 51°F | 42°F | 4.3" |
| December | 23°F | 37°F | 30°F | 3.5" |
| Index | Princeton | Illinois | National |
| Air quality index | 0 | 41 | 42 |
| Pollution index | 2,097,740 | 3,148,694 | 2,726,193 |
| Measurement | Total |
| Days measured | 335 |
| Days with good air quality | 334 |
| Days with moderate air quality | 1 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.001% |
| Benzene | 0.060% |
| Carbon Tetrachloride | 0.000% |
| Lead | 0.001% |
| Mercury | 0.300% |
| City | Population | Air Quality Index | National Avg. |
| Arlington, IL | 211 | 0 | 100.0% |
| McNabb, IL | 237 | 0 | 100.0% |
| Bureau Junction, IL | 220 | 0 | 100.0% |
| Mark, IL | 534 | 0 | 100.0% |
| Hollowayville, IL | 57 | 0 | 100.0% |
| Princeton, IL | 7,589 | 0 | 100.0% |
| City | Population | Air Quality Index | National Avg. |
| Corning, CA | 7,589 | 41 | 18.0% |
| Yreka, CA | 7,589 | 36 | 28.0% |
| Sioux Center, IA | 7,592 | 35 | 30.0% |
| Clear Lake, IA | 7,594 | 15 | 70.0% |
| Glen Ridge, NJ | 7,583 | 51 | 2.0% |
| Princeton, IL | 7,589 | 0 | 100.0% |
Here are the best places to live in Illinois
These are the 10 cheapest cities in Illinois
Check out the 10 most dangerous cities in Illinois
Most Dangerous States In The US