Sonoma County is on the northwest coast of California, one of the northernmost parts of the greater San Francisco Bay Area, U.S. Its population at the 2000 census was 458,614. Its largest city and county seat is Santa Rosa.

Sonoma is the southwestern county of California's Wine Country region, which also includes Napa, Mendocino, and Lake counties. It has thirteen approved American Viticultural Areas and over 250 wineries. In 2002 Sonoma County ranked as the thirty-second county in the United States in agricultural production. As early as 1920 Sonoma County was ranked as the eighth most productive U.S county, largely due to the abundance of high quality irrigation water. More than 7.4 million tourists visit each year, spending more than $1 billion in 2006. Sonoma County is the home of Sonoma State University and Santa Rosa Junior College.

In earlier times, Sonoma County was the home to several distinct Native American tribes, who lived within the carrying capacity of the land; by 1850, European settlement had set a new direction that would prove to radically alter the course of land use and resource management of this region. As of 2007, Sonoma County has rich agricultural land, albeit now largely divided between two nearly monocultural uses: grapes and pasturage. The voters have twice approved an open space initiative that has provided considerable funding for public acquisition of natural areas, which has preserved forested areas, coastal habitat, and other open space.