California County is a term used to describe the 58 counties in the state of California. Sonoma, Napa, and Marin are three of these counties. Sonoma County is located in the northern part of the state and is home to the city of Santa Rosa. Napa County is located in the northern part of the state and is known for its wine production. Marin County is located in the northern part of the state and is home to the cities of San Rafael and Novato.