Santa Clara County was one of the original counties of California, formed in 1850 at the time of statehood. The original inhabitants included the Ohlone, residing on Coyote Creek and Calaveras Creek. Part of the county's territory was given to Alameda County in 1853.
In the early 20th century, the area was promoted as the "Valley of the Heart's Delight" due to its natural beauty, including a significant number of orchards.
The first major technology company to be based in the area was Hewlett-Packard, founded in a garage in Palo Alto in 1939. IBM selected San Jose as its West Coast headquarters in 1943. Varian Associates, Fairchild Semiconductor, and other early innovators were located in the county by the late 1940s and 1950s. The U.S. Navy had a large presence in the area and began giving large contracts to Silicon Valley electronics companies. The term "Silicon Valley" was coined in 1971. The trend accelerated in the 1980s and 1990s, and agriculture has since then been nearly eliminated from the northern part of the county. Today, Santa Clara County is the headquarters for approximately 6500 high technology companies, including many of the largest tech companies in the world, among them hardware manufacturers AMD, Cisco Systems and Intel, computer and consumer electronics companies Apple Inc. and Hewlett-Packard, and internet companies eBay, Google, and Yahoo!. Most of what is considered to be Silicon Valley is located within the county, although some adjoining tech regions in San Mateo (e.g., Facebook), Alameda, and Santa Cruz counties are also considered part of Silicon Valley.
According to the U.S. Census Bureau, the county has a total area of 1,304 square miles (3,380 km2), of which 1,290 square miles (3,300 km2) is land and 14 square miles (36 km2) (1.1%) is water.
Tule elk roam the Diablo Range and are often seen on Coyote Ridge from U.S. Highway 101 - courtesy Bill Leikam
Three tule elk just north of U. S. Highway 101 in Basking Ridge Park. The freeway is a barrier to elk migration to the Coast Range. Courtesy Craige Edgerton
Both tule elk (Cervus canadensis nannodes) and pronghorn (Antilocapra americana) were historically native to Santa Clara County. In June 1776, Lieutenant Commander Don José Joaquín Moraga led a group of soldiers and colonists from the Presidio of Monterey to establish Mission San Francisco de Asis and encountered both tule elk and pronghorn, and clearly distinguished these two species from deer. The deer in California being California mule deer (Odocoileus hemionus).
Regarding elk, Moraga wrote: “In the great plain called San Bernardino (the Santa Clara Valley which stretches from south San Jose to Gilroy), while the expedition was strung out at length, we descried in the distance a herd of large animals that looked like cattle, but we could not imagine where they belonged or from whence they had come...with horns similar in shape to those of the deer, but so large that they measured sixteen palms from tip to tip.” Upon measurement, Morago reported the elk horns as four varas [11 feet] across… “These animals [elk] are called ciervos in order to differentiate them from the ordinary Spanish variety of deer, here called venados, which also exist in abundance and of large size in the vicinity.”
Regarding pronghorn, Moraga reported: “In the said plains of San Bernardino (Santa Clara Valley)…there is another species of deer about the size of three-year-old sheep. They are similar in appearance to the deer, except that they have short horns and also short legs like the sheep. They live in the plains where they go in herds of 100, 200, or more. They run all together over the plains so fast that they seem to fly…These animals are called berrendos and there are many of them also in the southern Missions wherever the country is level.”
Herbert Eugene Bolton also wrote of elk reports from another Spanish expedition, from the De Anza Expedition on March 23, 1776: " In Gilroy Valley (Santa Clara Valley) Moraga 's larder was replenished by three elks which the men killed without leaving the road." 
In 1978, California Department of Fish and Game warden Henry Coletto urged the department to choose the Mount Hamilton area as one of California's relocation sites under a new statewide effort to restore tule elk. While other ranchers refused, tech pioneers Bill Hewlett and David Packard allowed Coletto and state biologists to translocate the initial 32 tule elk from the Owens Valley in the eastern Sierra onto the 28,000-acre (11,000 ha) San Felipe Ranch, which the families jointly own, in the hills east of Morgan Hill. From the three original 1978–1981 translocations (totaling 65 animals) to the Mount Hamilton region of the Diablo Range, there are multiple herds in different locations including the Isabel Valley, San Antonio Valley, Livermore area, San Felipe Ranch, Metcalf Canyon, Coyote Ridge, Anderson Lake, and surrounding areas such as the Sunol and Cottonwood Creek (near San Luis Reservoir in western Merced County, California) herds. As of 2012, an estimated 400 tule elk roam 1,875 square kilometres (724 sq mi) in northeastern Santa Clara County and southeastern Alameda County. In March 2014 CDFW translocated nine bull elk from the San Luis National Wildlife Refuge to add genetic diversity to the San Antonio Valley Ecological Reserve herd in San Antonio Valley in extreme eastern Santa Clara County. As of 2017 there were four herds in the Coyote Ridge area, often visible from U. S. Highway 101, according to Craige Edgerton, recently retired executive director of the Silicon Valley Land Conservancy and local naturalist Michael Hundt. In 2019, a fifth herd of tule elk was documented by local naturalist Roger Castillo, likely having split from the Coyote Ridge herd and established itself in Silver Creek Valley around the closed Ranch Golf Club. The elk herds in eastern Santa Clara County are blocked from dispersal to the west by U.S. Highway 101, with environmentalists advocating re-purposing the Metcalf Road bridge at the Coyote Gap into a wildlife overcrossing. This would enable elk to recolonize rural southwestern Santa Clara County, as well as Santa Cruz and San Mateo Counties.
In 1990, the California Department of Fish and Game's Henry Coletto translocated excess pronghorn from Modoc County to six locations in California, including 51 animals to the San Felipe Ranch in Santa Clara County, where the swift-footed ungulates had not lived for generations. The animals left the San Felipe Ranch for the Isabel and San Antonio Valleys, as well as an area near Lake Del Valle in Alameda County may now be extirpated by poaching, highway vehicle collisions, and insufficient numbers to defend pronghorn fawns against coyote predation. As of 2012, the Isabel Valley Ranch herd had dwindled to 3 animals, and the Lake del Valle herd to 13. Currently, iNaturalist.org has zero observer records of pronghorn in Santa Clara County.
The Nature Conservancy "Mount Hamilton Project" has acquired or put under conservation easement 100,000 acres (40,000 ha) of land towards its 500,000 acres (200,000 ha) goal for habitat conservation within a 1,200,000 acres (490,000 ha) area encompassing much of eastern Santa Clara County as well as portions of southern Alameda County, western Merced and Stanislaus Counties, and northern San Benito County. Acquisitions to date include the 1,756-acre (711 ha) Rancho Cañada de Pala, straddling the Alameda Creek and Coyote Creek watersheds for California tiger salamander habitat; a conservation easement on the 3,259-acre Blue Oak Ranch Reserve, which abuts the north side of Joseph D. Grant County Park; a conservation easement on the 28,359-acre San Felipe Ranch, connecting Joseph D. Grant County Park with Henry W. Coe State Park; the 2,899-acre South Valley Ranch which protects a tule elk herd in the San Antonio Valley, and other properties.
As of 1980, Santa Clara County has the highest number of Superfund Sites of any county in the United States, accounting for 25 polluted locations requiring a long-term response to clean up hazardous material contaminations.[needs update] The vast majority of these Superfund sites were caused by firms associated with the high tech sector located in Silicon Valley.
Census demographics data released in 2019 shows that Asian-Americans have had the plurality of Santa Clara's population since 2014.
Thematic map showing median household income across central Santa Clara County
There were 565,863 households, out of which 34.9% had children under the age of 18 living with them, 54.9% were married couples living together, 10.0% had a female householder with no husband present, and 30.1% were non-families. 21.4% of all households were made up of individuals, and 5.9% had someone living alone who was 65 years of age or older. The average household size was 2.92 and the average family size was 3.41.
In the county, the population was spread out, with 24.7% under the age of 18, 9.3% from 18 to 24, 35.4% from 25 to 44, 21.0% from 45 to 64, and 9.5% who were 65 years of age or older. The median age was 34 years. For every 100 females there were 102.80 males. For every 100 females age 18 and over, there were 101.90 males.
The median income for a household in the county was $74,335, and the median income for a family was $81,717. Males had a median income of $56,240 versus $40,574 for females. The per capita income for the county was $32,795. About 4.9% of families and 7.5% of the population were below the poverty line, including 8.4% of those under age 18 and 6.4% of those age 65 or over.
Santa Clara County has five elected supervisors, elected within their districts.
The county is one among three counties in California (with Napa and Madera) to establish a separate department, the Santa Clara County Department of Corrections, to deal with corrections pursuant to California Government Code §23013.
Voters in the county also elect a number of other officials to county-wide positions, including the Santa Clara County District Attorney, the Santa Clara County Sheriff, and a large number of criminal and civil judges that serve in courts throughout the county.
Historically, Santa Clara County was a Republican stronghold in presidential elections. From 1872 through 1984, the only Democrats to carry Santa Clara County were Franklin Roosevelt, Lyndon Johnson, and Hubert Humphrey. Since 1988, Santa Clara County has been a Democratic stronghold in presidential and congressional elections. The last Republican to win a majority in the county was Ronald Reagan in 1984. While Republicans remained competitive at the state and local level throughout the 1990s, there are currently no elected Republicans representing the county above the local level.
Presidential election results
Santa Clara County vote by party in presidential elections
As of November 2012, all of the cities, towns, and the unincorporated areas of Santa Clara County have more registered Democrats than Republicans. In the 2008 US Presidential Election, Democratic nominee Barack Obama carried every city and town in the county, as well as the unincorporated areas.
Following the passage of Proposition 8, Santa Clara County joined San Francisco and Los Angeles in a lawsuit, becoming, along with San Francisco and Los Angeles, the first governmental entities in the world to sue for same-sex marriage.
The following table includes the number of incidents reported in 2009 and the rate per 1,000 persons for each type of offense. Law Enforcement in Santa Clara County is handled by the Santa Clara County Sheriff's Office.
The county's economy is heavily service based. Technology, both hardware and software, dominates the service sector by value, but like any other county, Santa Clara has its share of retail and office support workers.
The San Jose/Sunnyvale/Santa Clara metropolitan region, comprising Santa Clara County and San Benito County, was ranked as the highest performing metropolitan area in the US in 2012, ahead of Austin, Texas and Raleigh, North Carolina, according to the Milken Institute. The GDP of the metro area reached $176.7 billion in 2011, or $94,587 per capita, roughly on par with Qatar in both total GDP and per capita (nominal). GDP grew a strong 7.7% in 2011, and in contrast with most of California, GDP and per capita GDP (nominal) is well above 2007 (financial crisis) levels. Despite relative wealth vis a vis other regions nationally, a large underclass exists whose income is roughly equivalent to that elsewhere in the country, despite extreme land prices. The surge in metro GDP is highly correlated with home prices, which for average single-family homes passed $1 million ($1,017,528) in August 2013.
Santa Clara County Library, is a public library system serving the communities and cities of Campbell, Cupertino, Gilroy, Los Altos, Los Altos Hills, Milpitas, Monte Sereno, Morgan Hill, Saratoga, and all unincorporated areas of the county. All other cities run their own library system.
The county has an extensive freeway system and a separate expressway system (though it's not as extensive as those in Southern California). Expressways in California are distinct from freeways; although access to adjoining properties is eliminated, at-grade intersections are allowed. However, unlike expressways virtually everywhere else in California, the Santa Clara County expressways were built, signed, and maintained as county roads; they are not maintained by Caltrans, although they are patrolled by the California Highway Patrol.
There is also a large street network dominated by four- and six-lane arterials. Some of the newer boulevards (primarily in the West Valley) are divided with landscaped medians.
The county has no commercial seaports, although small boats can access San Francisco Bay from several points. Like many other Bay Area counties, it is dependent upon the Port of Oakland for transport of ocean cargo.
Santa Clara County Department of Correction is administered by the county's sheriff's office and supervises the following facilities:
Santa Clara County also contains Ulistac Natural Area, a volunteer maintained natural open space. Foreign and invasive species are removed when possible as native plants are introduced. Migratory birds and butterflies often use this area.
To promote friendship and understanding and to build bridges with countries of origin for various ethnic populations in the county, the County of Santa Clara has created a Sister County Commission to coordinate the program. As of 2009, there are three sister counties:
^ abcGeorge Ezra Dane and Francisco Palóu (June 1, 1935). "The Founding of the Presidio and Mission of Our Father Saint Francis". California Historical Quarterly. 14 (2): 102–110. doi:10.2307/25160571. JSTOR25160571.CS1 maint: uses authors parameter (link)
^Herbert Eugene Bolton (1930). Anza's California Expeditions Volume I. An Outpost of Empire. Berkeley, California: University of California Press. p. 393.