Diamond Bar is a city in eastern Los Angeles County, California, United States.

[9] It is named after the "diamond over a bar" branding iron registered in 1918 by ranch owner Frederic E. Lewis (1884–1963).

Located at the junction of the Pomona and Orange freeways, Diamond Bar is primarily residential with shopping centers interspersed throughout the city.

[10] Northern Diamond Bar is a part of the Pomona Unified School District.

[11] Southern Diamond Bar is a part of the Walnut Valley Unified School District.

[13] It also has the first hydrogen fueling station to be built in Southern California,[14] near the South Coast Air Quality Management District building.

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.

Linares died in 1847, and his widow sold a part of the ranch to Ricardo Vejar for $100 in merchandise, 100 calves, and the assumption of her late husband's debts.

The entire Diamond Bar Ranch was acquired by the Transamerica Corporation in the 1950s for the purpose of developing one of the nation's first master-planned communities.

Diamond Bar's main road, Diamond Bar Boulevard, runs along the bottom of the valley that eventually becomes Brea Canyon, and housing developments overlook the boulevard on both sides from surrounding hills.

Diamond Bar is also adjacent to the Inland Empire region, with Chino Hills directly to the east, and to the south of Diamond Bar lie the cities of Brea and La Habra in Orange County.

According to the United States Census Bureau, the city has a total area of 14.9 square miles (39 km2), with no significant bodies of water.

[34] The racial makeup of Diamond Bar was: Asian (61.0%); White (23.3%); Black or African American (4.0%); Hispanics and Latinos of any origin made up 17.8% of the overall population.

There were 18,455 housing units at an average density of 1,239.8 per square mile (478.7/km2), of which 14,513 (81.2%) were owner-occupied, and 3,367 (18.8%) were occupied by renters.

[39] Diamond Bar City Council is currently headed by Mayor Chia Yu Teng.

The other council members are Andrew Chou, Ruth Low, Stan Liu, and Steve Tye.

[41] The city is in the First District of the Los Angeles County Board of Supervisors, represented by Hilda Solis.