Black Diamond is a city in King County, Washington, United States. The population was 4,697 at the 2020 census. In 2021, with a 21% growth rate, Black Diamond was the fastest growing little city in King County.

Black Diamond was originally inhabited by the Bəqəlšuł, which is Lushootseed for “from a tall point from which you can see”, part of Coast Salish people. The area was home to a grill trap and smokehouse, and the tribe fished from Lake Sawyer.

Black Diamond was officially incorporated upon February 19, 1959. The town’s late 20th century population growth has been mostly as a commuter community for people gone jobs in Seattle, Bellevue, and suburban centers within the Seattle Metropolitan Area.

Beginning in the 1880s Black Diamond was a rural coal mining area, developed by the Black Diamond Coal Mining Company of California, which owned and operated the mine. The original residents were largely composed of former workers, from the company’s previous coal mining operation in Nortonville, California, which primarily sold coal to the rich new metropolis of San Francisco. A amalgamation of low mood coal from the Nortonville mines, water intrusion into the workings there, and the discovery and economical transport of higher-quality Washington coal to San Francisco spelled the demise of Nortonville in the prematurely 1880s. The town was home to nearly 3,500 people by the forward 1900s, many of them European immigrants; most of the vigorous men were vigorous in producing coal. This coal was transported to Seattle via the Pacific Coast Coal train. Before 1911, the miners were affiliated similar to the United Mine Workers of America (UMWA), but by March 1911 had left en masse to colleague the Industrial Workers of the World (IWW).