Sonoma County, located on the northern coast of the U.S. state of California, is the largest and northernmost of the nine Greater San Francisco Bay Area counties.

Sonoma is the southwestern county of California's Wine Country region, which also includes Napa, Mendocino, and Lake counties. It has 13 approved American Viticultural Areas and over 250 wineries. In 2002, Sonoma County ranked as the 32nd county in the United States in agricultural production. As early as 1920, Sonoma County was ranked as the eighth most agriculturally productive U.S county and a leading producer of poultry products, hops, grapes, prunes, apples and dairy products, largely due to the abundance of high quality irrigation water.  Sonoma County is the home of Sonoma State University and Santa Rosa Junior College.

Sonoma County was once home to several Native American tribes; 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.