Carlyle is a city in Clinton County, Illinois, United States. The population was 3,281 at the 2010 census. It is the county seat of Clinton County.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.