Trans-Mississippi was a common name of the geographic area west of the Mississippi River during the 19th century. The term "Trans-Mississippi" was historically used to refer to any land "across the Mississippi" (or the entire western two-thirds of the United States), including Nebraska, Iowa, North Dakota, South Dakota, Kansas, Minnesota, Arkansas, Louisiana, Missouri, Texas, New Mexico, Arizona, California, Nevada, Colorado, Montana, Idaho, Washington and Oregon. It also included Indian Territory (now Oklahoma), Alaska, Hawaii, and other U.S. territories. [1][2]
In 1898, a Trans-Mississippi Exposition was held in Omaha, Nebraska.