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 from Sacramento to Omaha in the United States 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 Central Pacific Railroad (CPRR) was a rail company chartered by U.S. Congress in 1862 to build a railroad eastwards from Sacramento, California, to complete most of the western part of the "First transcontinental railroad" in North America. Incorporated in 1861, CPRR ceased independent operations in 1875 when the railroad was leased to the Southern Pacific Railroad. Its assets were formally merged into Southern Pacific in 1959.