Tehama County was formed from parts of Butte, Colusa and Shasta Counties in 1856.

The county is named for the City of Tehama. Suggested possible roots are the Arabic word tehama ("hot low-lands"), the Spanish word tejamanil (shingle), or "high water" in the dialect of local Native Americans.

Famous early figures include Kit Carson, who took part in a fight that gave name to Bloody Island and Battle Creek, Jedidiah Smith, John Fremont, and William B. Ide, the first and only president of the California Republic.