Herlong is a census-designated place in Lassen County, California. It is located 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 north of Reno, Nevada, and about 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.
The postal stamps, money orders and equipment bore the spelling 'Hurlong' which lasted for about five days, when the error was corrected.
Since its beginning, the town has varied in size, peaking at about 5,000, in the 1950s (mostly civilian employees on the base), to the current population of 298 (at the 2010 census).
Herlong has numerous churches. These include Bible Baptist Church, which is an Independent Baptist church pastored by Michael Reed, an Assembly of God church, and a Southern Baptist church. The Office of Historic Preservation currently lists 62 historic properties in Herlong on its Historic Properties Data File for Lassen County.
Herlong is in Lassen County, which is one of the last counties in the west that is still considered "open range" land.
The Sierra Army Depot now serves as a munition and explosive disposal area, destroying approximately 53 million decommissioned explosives annually.