Carlyle is a city in and the county seat of Clinton County, Illinois, United States. The population was 3,253 at the 2020 census. Carlyle is located approximately 50 miles east of St. Louis, Missouri, and is home to Illinois' largest man-made lake, Carlyle Lake, and to the General Dean Suspension Bridge, a suspension bridge that is the only one of its kind in Illinois and crosses the Kaskaskia River.