is a city in Los Angeles County, California, United States. The population was about 60,360 as of January 1, 2008 . It is named after the "diamond over a bar" branding iron registered in 1918 by ranch owner Frederick E. Lewis.
Located at the junction of the Pomona and Orange freeways, Diamond Bar is primarily a residential city with shopping centers interspersed within the city. The city features a public Los Angeles County golf course.
Diamond Bar has the first hydrogen fueling station to be built in Southern California, near the South Coast Air Quality Management District (AQMD) building.
In 1840, Jose de la Luz Linares received the 4,340 acres (18 km²) Mexican land grant Rancho Los Nogales (Ranch of the Walnut Trees) from Governor Juan Alvarado. The land grant included Brea Canyon and the eastern Walnut Valley. 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 husbands debts. Vejar also owned the Rancho San Jose to the east, and acquired the rest of Rancho Nogales over the next 10 years.
But Vejar's luck did not last that long. As time wore on - and particularly as the United States government took over California - Rancho Los Nogales was divided and sold into multiple land ranches, the largest of which was the Diamond Bar Ranch. At the time, it was one of the largest working cattle ranches in the western U.S. 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. Transamerica gave the Diamond Bar name to its new community and incorporated the ranch's familiar diamond and bar cattle brand into various logos (many of which are still in use today).
The first tract homes went up in 1960, right next to where the Pomona Freeway (Route 60) would later pass. The town's development and population grew extremely fast after that.
Transamerica oversaw all development of the community through the 1960s. The Transamerica Corporation divested itself of all its real estate ventures in the 1970s and 1980s. As a result, the Diamond Bar project was sold to multiple developers and much of its initial master plan was not implemented during the latter half of its development in the 1980s.