Stewartville was an unincorporated

Unincorporated area

In law, an unincorporated area is a region of land that is not a part of any municipality.To "incorporate" in this context means to form a municipal corporation, a city, town, or village with its own government. An unincorporated community is usually not subject to or taxed by a municipal government...

 place in eastern Contra Costa County

Contra Costa County, California

Contra Costa County is a primarily suburban county in the San Francisco Bay Area of the U.S. state of California. As of the 2010 census, it had a population of 1,049,025...

, California

California

California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

 that is now a ghost town. It was located 6 miles (10 km) northeast of Mount Diablo, at an elevation of 558 feet (170 m). It was a mining town for the nearby coal mines.

A post office operated at Stewartville from 1882 to 1902. The place was named for William Stewart, coal mine owner.