Black Diamond is a town located in the Washington region of the United States. During the most recent census, Black Diamond had a population of 4,151. Black Diamond is the 183rd most poplulated city in the Washington region, the 6,986th most populated city in the United States and the 32,665th most populated city in the world. Black Diamond is in the America/Los Angeles timezone which is 7 hours behind UTC. Black Diamond adjusts the hour with daylight savings time during the winter months.