For thousands of years, the area was home to the Chumash tribe of Native Americans.

The Santa Barbara Channel received its name from Spanish explorer Sebastian Vizcaino when he sailed over the channel waters in 1602; he entered the channel on December 4, the day of the feast of Santa Barbara. He was not, however, the first European to enter the channel: that honor went to the Portuguese explorer Juan Rodriguez Cabrillo who arrived in 1542.

Mission Santa Barbara was founded on December 4, 1786 in what is now Santa Barbara. The county derives its name from the mission.

Santa Barbara County was one of the original counties of California, formed in 1850 at the time of statehood. Parts of the county's territory were given to Ventura County in 1872.