Santa Clara County was one of the original 18 counties incorporated in California in 1850 when the state became part of the United States. The Ohlone were the region's original inhabitants, residing on Calaveras Creek and Coyote Creek. Santa Clara County had extensive agriculture during the 19th and early 20th centuries. Spanish explorers and missionaries came to the region in the 18th century, and it became a Spanish mission in 1777. The missionaries established the Mission Santa Clara de Asis, which has continued to attract people wishing to learn about the county's history.

The region's natural beauty with its significant number of orchards during the early 1900s promoted the area as the "Valet of the Heart's Delight." The first technology company, Hewlett-Packard, started in 1939. In 1943 IBM selected the location for its West Coast headquarters. The presence of the U.S. Navy was integral to the county's growth because Silicon Valley electronics companies received many contracts from the maritime service branch. Since the late 20th century, the term "Silicon Valley" has become synonymous with the region, and agricultural activity has diminished significantly.

Santa Clara County, California, is currently home to more than 6500 high-tech companies, including some of the world's largest tech companies, such as Cisco Systems and Apple Inc.

Santa Clara County, California, received its name from Mission Santa Clara, established in 1777. The Spanish named the mission after Saint Clare of Assisi, Italy, in the late 18th century. Spain colonized California and set up a string of 21 churches. Franciscan padres (priests) selected the valley to establish the eighth mission. The valley was beautiful and fertile, and they named the mission, Mission Santa Clara for Saint Clare. However, linguists extended the name to mean the native Tamyen people gathered in the mission area and their primary language. The name Clara means bright or clear.