Shasta County was one of the original counties of California, created in 1850 at the time of statehood. Parts of the county’s territory were given to Siskiyou County in 1852, and to Tehama County in 1856.

The county was named after Mount Shasta; the name is derived from the English equivalent for the Shasta people, the name of a Native American tribe that once lived in the area. The name of the tribe was spelled in various ways until the present version was used when the county was established. Originally Mt. Shasta was within the county, but it is now part of Siskiyou County, to the north. Its 14,179-foot (4,322 m) peak is visible throughout most of Shasta County.