Below is a list of Williamson County IL zip codes. For your research we have also included Williamson County Area Code, Time Zone, UTC and the local County FIPS Code. Each Williamson County Illinois zip code has a center Longitude / Latitude point (the Williamson County center is -89.000198364258 / 37.776000976562). For your convenience we have also indicated if that zip code in Williamson County observes Daylight Savings time.