Diamond Bar is a city in eastern Los Angeles County, California, United States. The 2020 census listed a population of 55,072. It is one of a few cities in California with a majority Asian population (59.24% as of 2020). It is named after the "diamond over a bar" branding iron registered in 1918 by ranch owner Frederic E. Lewis (1884–1963). The city features a public Los Angeles County golf course. Located at the junction of the Pomona and Orange freeways, Diamond Bar is primarily residential with shopping centers interspersed throughout the city. It is surrounded by the cities of Brea, Walnut, Chino Hills, Pomona, City of Industry, and the unincorporated areas of Rowland Heights and South Diamond Bar. Northern Diamond Bar is a part of the Pomona Unified School District. Southern Diamond Bar is a part of the Walnut Valley Unified School District. The city is also served by International Polytechnic High School. It also has the first hydrogen fueling station to be built in Southern California, near the South Coast Air Quality Management District building.