Fort Madison is a city and a county seat of Lee County, Iowa, United States along with Keokuk. Of Iowa's 99 counties, Lee County is the only one with two county seats. The population was 10,270 at the time of the 2020 census. Located along the Mississippi River in the state's southeast corner, it lies between small bluffs along one of the widest portions of the river.

Lee County is the southernmost county in the U.S. state of Iowa. As of the 2020 census, the population was 33,555. The county seats are Fort Madison and Keokuk. Lee County is part of the Fort Madison–Keokuk, IA–IL–MO Micropolitan Statistical Area. It was established in 1836.