Napa County is a county located north of San Pablo Bay in the U.S. state of California. As of the 2010 census, the population was 136,484. The county seat is Napa. Napa County was one of the original counties of California, created in 1850 at the time of statehood. Parts of the county's territory were given to Lake County in 1861. Napa County comprises the Napa, CA Metropolitan Statistical Area, which is also included in the San Jose-San Francisco-Oakland, CA Combined Statistical Area It is one of four North Bay counties.