Glendora mostly lies within the San Gabriel Valley, area code 626. There are portions that are in the area code 909, which is the area code for western San Bernardino County; areas in eastern Los Angeles County, like Pomona; and parts of Riverside County, like Moreno Valley. The city to Glendora's west is Azusa while San Dimas lies to Glendora's east.
Don Palomares received a 15,000 acre (61 km²) land grant from Governor Juan Bautista Alvarado in 1837, which included the land of present day cities Pomona, Claremont, La Verne, San Dimas, and Glendora. This holding was called Rancho San Jose.
Located beneath the San Gabriel Mountains, modern Glendora was founded on April 1, 1887 by George D. Whitcomb who moved to California from Illinois in the early 1880s. Whitcomb was the founder of the Whitcomb Locomotive Works in Chicago and Rochelle, Illinois. He devised the name Glendora by combining the name of his wife, Leadora Bennett Whitcomb, with the location of his home in a glen of the San Gabriel Mountains. Prior to its 1911 incorporation, Glendora's administrator officially occupied the office of President of Glendora.
As of the censusGR2 of 2000, there were 49,415 people, 16,819 households, and 12,866 families residing in the city. The population density was 996.8/km² (2,581.5/mi²). There were 17,145 housing units at an average density of 345.9/km² (895.7/mi²). The racial makeup of the city was 80.30% White, 1.50% Black or African American, 0.65% Native American, 6.20% Asian, 0.08% Pacific Islander, 7.24% from other races, and 4.03% from two or more races. 21.7% of the population were Hispanic or Latino of any race.
There were 16,819 households out of which 38.6% had children under the age of 18 living with them, 60.1% were married couples living together, 12.1% had a female householder with no husband present, and 23.5% were non-families. 19.1% of all households were made up of individuals and 7.9% had someone living alone who was 65 years of age or older. The average household size was 2.88 and the average family size was 3.30.
In the city the population was spread out with 27.6% under the age of 18, 7.6% from 18 to 24, 29.1% from 25 to 44, 23.2% from 45 to 64, and 12.5% who were 65 years of age or older. The median age was 37 years. For every 100 females there were 93.2 males. For every 100 females age 18 and over, there were 89.6 males.
The median income for a household in the city was $60,013, and the median income for a family was $66,674. Males had a median income of $49,548 versus $35,062 for females. The per capita income for the city is $25,993. 5.9% of the population and 3.9% of families are below the poverty line. Out of the total people living in poverty, 6.7% are under the age of 18 and 5.0% are 65 or older.
Notable families and residents of Glendora have included: