Leavenworth (lĕvˈənwûrthˌ) [key], city (1990 pop. 38,495), seat of Leavenworth co., NE Kans., on the Missouri River; inc. 1855. It is the commercial center of a farm and livestock region, with flour mills and plants making automobile batteries, machinery, furniture, and metal products. Nearby Fort Leavenworth, with its various institutions (including the federal penitentiary), is central to the city's economy. The oldest city in Kansas, Leavenworth was the first city in the state to be incorporated. It was settled (1854) near the fort by proslavery Missourians but supported the Union during the Civil War. It flourished as a supply point on westward travel routes. The state's first newspaper was printed there in 1854. St. Mary College is nearby.