Fort Madison, city (1990 pop. 11,618), seat of Lee co., SE Iowa, on the Mississippi River; inc. 1838. Fort Madison, a U.S. trading post, was established in 1808 as the first fort west of the Mississippi; it was named for James Madison, then President. The city is a river port for barge traffic as well as a rail, commercial, and industrial center with a wide variety of light manufactures. Iowa State Penitentiary (1839) and Lee County Courthouse (1841) are in Fort Madison.