Black Diamond is a city in King County, Washington, United States. The population was 4,151 at the 2010 census.

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 native residents were largely composed of former workers, from the company’s previous coal mining operation in Nortonville, California, which primarily sold coal to the thriving new metropolis of San Francisco. A interest of low air 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 to the fore 1880s. The town was home to regarding 3,500 people by the prematurely 1900s, many of them European immigrants; most of the vigorous men were on the go in producing coal. This coal was transported to Seattle via the Pacific Coast Coal train. Before 1911, the miners were affiliated as soon as the United Mine Workers of America (UMWA), but by March 1911 had left en masse to associate the Industrial Workers of the World (IWW).

After World War I, the town shut the length of the mine as it was no longer viable. However a second mining boom spurred buildup in the town in the before 1930s upon the strength of combined mining operations promoted by the Morris brothers through the Palmer Coking Coal Company. Mining has continued until recently through the Pacific Coast Coal Company, formerly of San Francisco. The prospect of unconventional mining operations remains strong.

The main building of the Black Diamond Historical Museum is the former train station, which served the Columbia & Puget Sound Railway 1884–1916 and the Pacific Coast Railway 1916–1951. Regular passenger further ended in 1925, but a train still brought men to the mine until 1931, and trains continued to haul coal and freight into the 1940s.

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