Alton is a city on the Mississippi River in Madison County, Illinois, United States, about 15 mi north of St. Louis, Missouri. The population was 27,865 at the 2010 census. It is a part of the Metro-East region of the Greater St. Louis metropolitan area. It is famous for its limestone bluffs along the river north of the city, for its role preceding and during the American Civil War, and as the home town of jazz musician Miles Davis and Robert Wadlow, the tallest known person in history. It was the site of the last Abraham Lincoln and Stephen Douglas debate in October 1858. The former state penitentiary in Alton was used during the Civil War to hold up to 12,000 Confederate prisoners of war.