Fort Jefferson was a southwestern Ballard county town on the Mississippi River about one mile south of Wickliffe. It was founded in 1858 near the site of George Rogers Clark's 1780 fort, which became known as Clarksville, and was occupied until 1781. The Fort Jefferson post office opened in 1860, but moved to the new town of Wickliffe in 1879. A later Fort Jefferson post office operated from 1891 to 1892. The town is gone and the site is now the home of the Westvaco paper factory.