Sonoma County

Sonoma County is an administrative division in northern California, reaching from the Pacific coast to inland valleys and hills. The territory covers about 4,579 square kilometers (1,768 square miles) with nine incorporated cities, including Santa Rosa as the largest community and seat of government.

The county formed in 1850 as one of California's original counties after the state joined the Union. Santa Rosa became the administrative seat in 1854 and developed into the regional center.

The name comes from Pueblo de Sonoma, a former mission settlement at the northern end of California's mission trail. Many places carry Spanish names that reflect the early settlement period and remain in everyday use.

A public bus network connects all nine cities and many smaller communities, with Santa Rosa serving as a central hub. Coastal areas tend to be cooler and foggier than inland valleys, so bringing layered clothing is advisable.

The region hosts several geothermal power plants that tap into natural underground steam to generate electricity. These facilities sit in the Mayacamas mountain range and supply power to surrounding communities.

Location: California

Inception: 1850

Capital city: Santa Rosa

Shares border with: Mendocino County, Lake County, Napa County, Solano County, Marin County

Website: https://sonomacounty.ca.gov

GPS coordinates: 38.51000,-122.93000

Latest update: December 4, 2025 19:02