Carlyle is a city in Clinton County, Illinois, United States. The population was 3,253 at the 2020 census. It is the county seat of Clinton County. Carlyle is located approximately 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. History In 1811 or 1812, a man named John Hill built one of several "block" houses along the Goshen Trail, located at what is currently 201 Fairfax Street. The houses were reportedly built to serve as a line of defense against Native Americans. John Hill built the first house to be located in what has become Carlyle. He also established what could be considered Carlyle's first business: a ferry to carry traffic across the Kaskaskia River, including a small shelter at the river which served as a toll house. In 1816, Charles Slade and two of his brothers reached the John Hill settlement and bought him out. Charles farmed the land, took over the ferry, and within a year partnered with a man named Hubbard to start the first store, a mercantile business located at what is now 301 Fairfax Street. In 1818, a man named Calvin Barnes laid out town lots. On March 10, 1819, a post office was first established under the name Carlisle, Illinois. This spelling might have been a clerical error. The area was settled after the 1809 creation of the Illinois Territory but before Illinois achieved statehood, six to seven years after John Hill had already built his establishment. Illinois' first state capitol was located in Kaskaskia, but in 1820 the state decided that it should be moved. Carlyle lost to Vandalia by one vote. In 1824, the State of Illinois created Clinton County by carving it out of Washington, Bond, and Fayette counties. Carlyle was to be the county seat should land be donated for this purpose. Charles Slade donated of property so that the county seat would be located in Carlyle. Carlyle was founded in 1818 by Charles W. Slade, father of Joseph "Jack" Slade, who named the town after his grandmother's family. It was incorporated as a town on 2/10/1837 and incorporated as a city on 4/17/1884. Carlyle celebrated 150 years and used the 1837 date. Charles Slade pushed hard for Carlyle