contra_costa_county,_california | ispartof | san_francisco_bay_area <tsp> antioch,_california | ispartof | california <tsp> antioch,_california | ispartof | contra_costa_county,_california <tsp> california | language | chinese_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. in the san francisco bay area of california. chinese is one of the languages spoken in california.contra costa county california is in the east bay of the san francisco bay area