contra_costa_county,_california | ispartof | san_francisco_bay_area <tsp> antioch,_california | ispartof | california <tsp> antioch,_california | ispartof | contra_costa_county,_california <tsp> antioch,_california | leadertitle | united_states_house_of_representatives <tsp> california | language | spanish_language <sep> contra costa county ( (listen); contra costa, spanish for 'opposite coast') is a county located in the us state of california, in the east bay of the san francisco bay area as of the 2020 united states census, the population was 1,165,927 the county seat is martinez it occupies the northern portion of the east bay region of the san francisco bay area and is primarily suburban 
antioch. is part of contra costa county. which in turn. is part of the san francisco bay area. in california. where spanish is spoken. the united states house of representatives. is the leader title of antioch.contra costa county is in the u.s. state of california and spanish for 'opposite coast'