Tehama County is located in the northern part of the U.S. state of California. It is bisected by the Sacramento River. The county seat is Red Bluff.
The county has a total area of 2,962 mi², 99.6% of it is land and 0.4% of it is water. As of the census of 2000, there were 56,039 people, 21,013 households, and 14,898 families residing in the county. The population density was 19/mi². The median age was 38 years. The median income for a household in the county was $31,206, and the median income for a family was $37,277.