Leavenworth is the largest city and county seat of Leavenworth County, in the U.S. state of Kansas and is located near Kansas City, Missouri. Located in the northeast portion of the state, it is situated on the west bank of the Missouri River. The population was 35,420 at the 2000 census. Leavenworth, founded in 1854, was the first incorporated city in Kansas. Leavenworth apartments for rent comparison page shows most up to date rent information on Leavenworth apartments and houses. Rent information is obtained from multiple rental sources but we cannot guarantee their accuracy.