The mission of the Black Diamond Historical Society shall be the discovery, preservation, and dissemination of the history of Black Diamond and environs, as it relates to King County and the State of Washington. The Black Diamond Museum is open every Thursday, 9 AM – 4 PM, and weekends from noon – 4 PM (summertime) and noon – 3 PM (winter). The Museum is closed over the Christmas holiday – December 16 – January 3.