Santa Clara County, officially the County of Santa Clara, is the sixth-most populous county in the U.S. state of California, with a population of 1,936,259, as of the 2020 census. Santa Clara County and neighboring San Benito County together form the U.S. Census Bureau’s San Jose-Sunnyvale-Santa Clara metropolitan statistical area, which is part of the larger San Jose-San Francisco-Oakland combined statistical area. Santa Clara is the most populous county in the San Francisco Bay Area and in Northern California. The county seat and largest city is San Jose; with about 1,000,000 residents, it is the 10th-most populous city in the United States, California’s third-most populous city and the most populous city in the San Francisco Bay Area. The second- and third-largest cities are Sunnyvale and Santa Clara.

Home to Silicon Valley, Santa Clara County is an economic center for high technology, and in 2015 had the third-highest gross domestic product (GDP) per capita in the world (after Zürich, Switzerland and Oslo, Norway), according to the Brookings Institution. Located on the southern coast of San Francisco Bay, the urbanized Santa Clara Valley within Santa Clara County contains most of the county’s population. More recently, extensive droughts in California, further complicated by drainage of the Anderson reservoir within the county for seismic repairs, have strained the county’s water security.

The county’s concentration of wealth, primarily due to the tech industry, has made it the most affluent county on the West Coast of the United States and the most affluent outside the Washington metropolitan area and one of the most affluent places in the United States.

Santa Clara County is named for Mission Santa Clara, which was established in 1777, and was in turn named for Saint Clare of Assisi.

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 1882, Santa Clara County tried to levy taxes upon property of the Southern Pacific Railroad within county boundaries. The result was the U.S. Supreme Court case of Santa Clara County v. Southern Pacific Railroad, 118 U.S. 394 (1886), in which the court extended due-process rights to artificial legal entities.

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 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 been nearly eliminated from the northern part of the county.

Today, Santa Clara County is the headquarters for about 6,500 high-technology companies, including many of the largest ones in the world, among them hardware manufacturers AMD, Nvidia, 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 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, of which 14 square miles (1.1%) are covered by water.

Counties which border with Santa Clara County are, clockwise, Alameda County, San Joaquin (within a few hundred feet at Mount Boardman), Stanislaus, Merced, San Benito, Santa Cruz, and San Mateo County. Santa Clara County formerly shared borders with Contra Costa, San Francisco, Mariposa, Monterey, and Tuolumne counties until 1853, 1856, 1874, and 1854 respectively (Monterey County currently comes within a few miles of Santa Clara).

The San Andreas Fault runs along the Santa Cruz Mountains in the south and west of the county.