The history of the Union Pacific Railroad stretches from 1862 to the present. For operations of the current railroad, see Union Pacific Railroad; for the holding company that owns the current railroad, see Union Pacific Corporation.
There have been four railroads called Union Pacific: Union Pacific Rail Road, Union Pacific Railway, Union Pacific Railroad (Mark I), and Union Pacific Railroad (Mark II). This article covers the Union Pacific Rail Road (UPRR, 1862–1880), Union Pacific Railway (1880–1897), and Union Pacific Railroad (Mark I)(UP, 1897–1998). For the history of the Union Pacific Railroad (Mark II), see Union Pacific and Southern Pacific Transportation Company.