El Sobrante lies within unincorporated Contra Costa County. Main roads include San Pablo Dam Road (a major road running from Richmond and San Pablo, through El Sobrante, past EBMUD's and San Pablo Reservoir), Valley View Road and Appian Way. San Pablo Dam Road and Appian Way both connect to Interstate 80 to the west.
Between 5,000 B.C. and 1,000 B.C., an indigenous tribe of people called the Huchiun, a sub-tribe of the Ohlone, came to the East Bay, including El Sobrante. One of the Huichin villages was located where the El Sobrante Library now stands. The Huichin left a now-buried shell mound beside San Pablo Creek.
In the 1770s, the Huchiun were forcefully converted to Christianity by Spanish missionaries, and died in great numbers. After Mexican independence from Spain in the early 19th century, Spanish colonists were given land grants, one of which was "Rancho El Sobrante", deeded to Juan Jose and Victor Castro in 1841. The grant's boundaries were unusually complicated as they were to be determined by the boundaries of the surrounding grants: San Antonio, San Pablo, El Pinole, La Boca de la Cañada del Pinole, Acalanes, and La Laguna de los Palos Colorados. In this sense, the rancho was el sobrante, the remaining area. Legal disputes concerning the borders and the claims of squatters continued for four decades, with much of the land sold to pay court and attorney costs. Victor Castro was left with 549 acres of the original grant. He built an adobe dwelling in what is now El Cerrito, and became one of the first members of the Board of Supervisors of Contra Costa County. Castro died at the age of 90 in 1897. Some of his descendants still live in the area of Castro Ranch Road.
El Sobrante was being called "Oak Grove" by industrial concerns in 1887 when the California and Nevada Railroad put a spur into the area for the purpose of carrying lumber cut from the hills.
By the early 20th century, Rancho El Sobrante had been reduced to a number of smaller ranches generally following a dirt road along San Pablo Creek. Many of these ranches were further subdivided. Roads were paved and homes were constructed. El Sobrante changed from a rural to a semi-rural community.
There were 4,676 households out of which 32.6% had children under the age of 18 living with them, 47.6% were married couples living together, 14.8% had a female householder with no husband present, and 32.2% were non-families. 24.6% of all households were made up of individuals and 8.3% had someone living alone who was 65 years of age or older. The average household size was 2.61 and the average family size was 3.11.
In the CDP the population was spread out with 24.7% under the age of 18, 7.3% from 18 to 24, 31.0% from 25 to 44, 25.2% from 45 to 64, and 11.8% who were 65 years of age or older. The median age was 38 years. For every 100 females there were 94.1 males. For every 100 females age 18 and over, there were 92.2 males.
The median income for a household in the CDP was $48,272, and the median income for a family was $59,342. Males had a median income of $44,232 versus $34,661 for females. The per capita income for the CDP was $24,525. About 6.6% of families and 9.5% of the population were below the poverty line, including 9.5% of those under age 18 and 10.7% of those age 65 or over.
El Sobrante is also home to a growing Sikh population, one of the largest in the San Francisco Bay Area and western United States. The center of the Sikh community is the Gurdwara Sahib of El Sobrante (known for its large golden dome) which sits high in the hills above San Pablo Dam Road.
Definition of an "El Sobrante fortnight" has yet to be determined, but reliable sources place the time span as somewhere between two weeks and a decade.