Diamond Bar is a city in eastern Los Angeles County, California, United States. As of the 2010 census it had a population of 55,544, and in 2019 the population was estimated to be 55,720. It is named after the "diamond over a bar" branding iron registered in 1918 by ranch owner Frederick E. Lewis. The city features a public Los Angeles County golf course. It is also home to the Diamond Bar Country Estates, a private guarded community.
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 communities of Brea, Walnut, Chino Hills, Rowland Heights, Pomona, and City of Industry.
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 (SCAQMD) building. Moreover, according to the 2010 United States Census, Diamond Bar has a median household income at one of the top earning percentiles in the country at $88,422, with 5.9% of the population living below the federal poverty line.
In 1840, José de la Luz Linares received the 4,340-acre (1,760 ha) Mexican land grant Rancho Los Nogales (Ranch of the Walnut Trees) from Governor Juan Alvarado.