Port Costa is a census-designated place (CDP) in Contra Costa County, California, United States. The population was 190 at the 2010 census.
Port Costa was founded in 1879 as a landing for the railroad ferry Solano, owned and operated by the Central Pacific Railroad.This put Port Costa on the main route of the transcontinental railroad. The Solano, later joined by the Contra Costa, carried entire trains across the Carquinez Strait from Benicia to Port Costa, from whence they continued on to the Oakland Pier. For a time, it was also the United States' busiest wheat-shipping port and had a reputation as a colorful, sometimes violent community.