Azusa is a city in the San Gabriel Valley, at the foot of the San Gabriel Mountains in Los Angeles County, California, United States.
The population was 46,361 at the 2010 census, up from 44,712 at the 2000 census. Azusa is located along historic Route 66, which passes through the city on Foothill Boulevard and Alosta Avenue.
Azusa is bordered by the San Gabriel Mountains range to the north, Irwindale to the west, the unincorporated community of Vincent to the southwest, Glendora and the unincorporated community of Citrus to the east, and Covina to the south. The A on the San Gabriel Mountains represents the city of Azusa, and can be seen within a 30-mile radius.
"Azusa stands for everything from A to Z in the U.S.A." has been a phrase used to promote the city by organisations such as the Chamber of Commerce for many years. The place name "Azusa" dates to the Mexican Alta California era in the 19th century when Azusa was used to refer to the San Gabriel Valley and the San Gabriel River. It appears to have been derived from the Tongva place name Asuksagna. The area was part of the Tongva peoples (Gabrieleño Indians) homeland since at least 55 BC.
The first Mexican settlement in Azusa was at the Rancho el Susa in 1841, a Mexican land grant from the Alta California Governor Juan Bautista Alvarado to Luis Arenas. In 1844 Arenas sold the rancho's land to Henry Dalton, an English immigrant and wealthy merchant from the Pueblo of Los Angeles, for $7,000. He renamed it Rancho Azusa de Dalton, and had built a winery, distillery, vinegar house, meat smokehouse, and flour mill.