As of 4:08 PM CST on December 16, 2025, all 16 cities in Williamson County, IL in our database have a UV Index reading of Low. The city with the highest UV Index reading right now is Marion, IL with a reading of 0.2.
Over the next 24 hours, the highest UV Index reading in Williamson County, IL is expected to be 2.1 in Marion between 12:00 PM - 1:00 PM CST tomorrow.
| Range | 0 - 2 | 3 - 5 | 6 - 7 | 8 - 10 | 11+ |
|---|---|---|---|---|---|
| Color | |||||
| Risk | Low | Moderate | High | Very High | Extreme |