Robert Stockton Williamson (January 21, 1825 – November 10, 1882) was an American soldier and engineer, noted for conducting surveys for the transcontinental railroad in California and Oregon.

Inducted into the Army Corps of Engineers in 1861, he had a distinguished record serving in the American Civil War, winning two brevet promotions.

In 1853, War Secretary Jefferson Davis chose Williamson to lead surveys of California's southern Sierra and mountains near Los Angeles for the Pacific Railroad.

[1] Williamson was then assigned to the staff of the commanding general of the Department of the Pacific, and was the engineer in charge of the military roads in southern Oregon.

In 1866, Major Williamson was appointed Commander and Officer-in-Charge when the U. S. Army Corps of Engineers established its San Francisco District Office in 1866.

This office was then mainly responsible for engineering related to rivers and harbors along the entire Pacific coast, from Canada to Mexico, and included Hawaii.