Herlong is a census-designated place in Lassen County, California. It is located 8 miles (13 km) north of Doyle, at an elevation of 4114 feet (1254 m). Herlong is located in southern Lassen County near the southeast edge of Honey Lake about 70 miles (110 km) north of Reno, Nevada, and about 45 miles (72 km) south of Susanville. The community is accessible to U.S. Route 395 via Lassen County Route A25 or Lassen County Route A26.
Herlong is located at the extreme Eastern edge of the Sierra Nevada Mountain Range in the southeastern region of Honey Lake Valley.
Herlong is a town built to house civilian workers for Sierra Army Depot, which was built in 1942. Sierra Army Depot was one of several ammunition storage facilities located far enough inland to be safe from Japanese attack. The site also met the requirement that the depot be in a dry and isolated area. Herlong was named after Captain Henry W. Herlong, the first Army ordnance officer to die in WWII.