Watseka is a city in and the county seat of Iroquois County, Illinois, United States. It is located approximately 15 miles (24 km) west of the Illinois-Indiana state line on U.S. Route 24. The city population was 5,670 at the time of the 2000 census. The south half is in Belmont Township; the north half is in Middleport Township. Incorporated in 1865, Watseka is named for a Potawatomi Native American woman Watseka (Watchekee).