American civil engineer who was a central figure in the original promotion, establishment, and design of the First Transcontinental Railroad.

He found investors for what became the Central Pacific Railroad (CPRR). As chief engineer, he performed much of the route survey work to determine the best alignment for the railroad over the Sierra Nevada, which was completed six years after his death.

• Mount Judah, an 8,245-foot peak in Placer County, CA, located adjacent to Donner Peak and Mount Lincoln in the Sierra Nevada Tahoe National Forest, was formally named for Judah on October 18, 1940 by the U.S. Board on Geographic Names. Running through the mountain about 1,000 below the summit is the 10,322-foot long single track UPRR Sierra Grade Tunnel #41 (aka "The Big Hole") which was opened in 1925 and carries both UPRR freight and Amtrak passenger trains in both directions over Donner Summit between Soda Springs and Eder. This route bypasses the original, now abandoned 1868 CPRR "Summit Tunnel" (#6) surveyed by Judah which is located a mile to the north and had remained in service until 1993.
• Judah Street in San Francisco and its N-Judah Muni streetcar line are named after him. Memorial plaques dedicated to him have been erected in Folsom and Sacramento, California
• Elementary schools in Sacramento and Folsom are named after Judah.