Del Mar is a beach town in San Diego County, California, located on the coast of the Pacific Ocean. Established in 1885 as a seaside resort, the city incorporated in 1959. The Del Mar Horse Races ar…Del Mar is a beach town in San Diego County, California, located on the coast of the Pacific Ocean. Established in 1885 as a seaside resort, the city incorporated in 1959. The Del Mar Horse Races are hosted on the Del Mar racetrack every summer.