Home > Leavenworth Convention & Visitors Bureau Leavenworth Convention & Visitors Bureau 518 Shawnee, P.O. Box 44, Leavenworth, Kansas 66048 (913) 682‐4113 Leavenworth is the "First City incorporated in the state of Kansas" and Fort Leavenworth is known as the "Post that opened the West" and is the oldest fort in continuous use west of the Mississippi River. Tweet Pin It