The Union Pacific railway is a current operating railway company west of the Mississippi River. Currently, Union Pacific is the largest operating railway network in the United States. Former mergers of the company were, Chicago and Northwestern, Missouri Pacific, Western Pacific, Missouri-Kansas-Texas, Southern Pacific Lines, and Denver and Rio Grande Western. Union Pacific currently owns 26% of Ferromex While Grupo Mexico owns the remaining 74%. Union Pacific rosters (Former "patch numbered" locomotives): 37 Chicago and Northwestern, 445 Southern Pacific, 47 St. Louis and Southwestern (Cotton Belt), and 23 Denver and Rio Grande Western. Burlington Northern Santa Fe covers much of the same territory.

Dates of operation: 1862-present