Leavenworth is the county seat and largest city of Leavenworth County, Kansas, United States and is part of the Kansas City metropolitan area. As of the 2010 census, the city population was 35,251. It is located on the west bank of the Missouri River. The site of Fort Leavenworth, built in 1827, the city became known in American history for its role as a key supply base in the settlement of the American West. During the American Civil War, many volunteers joined the Union Army from Leavenworth. The city has been notable as the location of several prisons, particularly the United States Disciplinary Barracks and United States Penitentiary, Leavenworth.
Leavenworth, founded in 1854, was the first city incorporated in the territory of Kansas. The city developed south of Fort Leavenworth, which was established as Cantonment Leavenworth in 1827 by Colonel Henry Leavenworth. Its location on the Missouri River attracted refugee African-American slaves in the antebellum years, who were seeking freedom from the slave state of Missouri across the river. Abolition supporters helped them find refuge. In the years before the American Civil War, Leavenworth was a hotbed of anti-slavery and pro-slavery agitation, often leading to open physical confrontations on the street and in public meetings.
On April 3, 1858, the "Leavenworth Constitution" for the state of Kansas was adopted here.