The First transcontinental railroad, linking the eastern and western United States, is completed at Promontory Summit, Utah Territory with the golden spike.

America's first transcontinental railroad was a 1,911-mile (3,075 km) continuous railroad line built between 1863 and 1869 that connected the existing eastern U.S. rail network at Council Bluffs, Iowa, with the Pacific coast at the Oakland Long Wharf on San Francisco Bay. The rail line was built by three private companies over public lands provided by extensive U.S. land grants. Building was financed by both state and U.S. government subsidy bonds as well as by company-issued mortgage bonds. The Western Pacific Railroad Company built 132 miles (212 km) of track from the road's western terminus at Alameda/Oakland to Sacramento, California. The Central Pacific Railroad Company of California (CPRR) constructed 690 miles (1,110 km) east from Sacramento to Promontory Summit, Utah Territory. The Union Pacific Railroad (UPRR) built 1,085 miles (1,746 km) from the road's eastern terminus at the Missouri River settlements of Council Bluffs and Omaha, Nebraska, westward to Promontory Summit.

Promontory is an area of high ground in Box Elder County, Utah, United States, 32 mi (51 km) west of Brigham City and 66 mi (106 km) northwest of Salt Lake City. Rising to an elevation of 4,902 feet (1,494 m) above sea level, it lies to the north of the Promontory Mountains and the Great Salt Lake. It is notable as the location of Promontory Summit, where the first transcontinental railroad in the United States, from Sacramento to Omaha, was officially completed on May 10, 1869. The location is sometimes confused with Promontory Point, a location further south along the southern tip of the Promontory Mountains. Both locations are significant to the Overland Route: Promontory Summit was where the original, now abandoned, alignment crossed just north of the Promontory Mountains; while Promontory Point is where the modern alignment, called the Lucin Cutoff, crosses the southern tip of the Promontory Mountains.

The Territory of Utah was an organized incorporated territory of the United States that existed from September 9, 1850, until January 4, 1896, when the final extent of the territory was admitted to the Union as the State of Utah, the 45th state. At its creation, the Territory of Utah included all of the present-day State of Utah, most of the current state of Nevada save for a portion of Southern Nevada, much of modern western Colorado, and the extreme southwest corner of present-day Wyoming.