Monterey County was one of the original counties of California, created in 1850 at the time of statehood. Parts of the county were given to San Benito County in 1874. The area was originally populated by Ohlone, Salinan and Esselen tribes.

The county derives its name from Monterey Bay. The bay was named by Sebastián Vizcaíno in 1602 in honor of the Conde de Monterrey (or Count of Monterrey), then the Viceroy of New Spain. Monterrey is a variation of Monterrei, a municipality in the Galicia region of Spain where the Conde de Monterrey and his father (the Fourth Count of Monterrei) were from.