Somersville is an unincorporated ghost town in eastern Contra Costa County, California, USA.
Somersville was founded in the 1850s by gold miners. The town is no longer populated and is within the boundaries of the East Bay Regional Park District's Black Diamond Mines Regional Park. Somersville Road was named after the town; it is a major north-south arterial trunk road in the closest existing neighbor: Antioch. Somersville's ruins contain a fairly extensive amount of graves in its cemetery, many of whom are dead miners who died in accidents in the coal mines. The Somersville mines are now sealed to prevent entry due to frequent incidents of people becoming lost inside them during the mid 20th century.