Siskiyou County is a county located in the far northernmost part of the U.S. state of California, in the Shasta Cascade region on the Oregon border. Yreka is the county seat. Because of its substantial natural beauty, outdoor recreation opportunities, and Gold Rush era history, it is an important tourist destination within the state.

Siskiyou County was created on March 22, 1852, from parts of Shasta and Klamath Counties, and named after the Siskiyou mountain range. Parts of the county's territory were given to Modoc County in 1855. In 1851, after the discovery of an important gold strike near today’s Yreka, California, thousands of prospectors flooded the area. This era and setting was described in detail in the semi-autobiographical novel, Life Amongst the Modocs, written by poet and novelist Joaquin Miller.