Ventura County is a county in the southern part of the U.S. state of California. As of the 2010 census, the population was 823,318. The largest city is Oxnard, and the county seat is the city of Ventura.

Ventura County comprises the Oxnard-Thousand Oaks-Ventura, CA Metropolitan Statistical Area, which is also included in the Los Angeles-Long Beach, CA Combined Statistical Area. It is also considered the southernmost county along the California Central Coast.

Ventura County has been named the "most desirable" place to live in the U.S. by the Washington Post and the U.S. Department of Agriculture in 2015. It is home to several of the safest communities in the U.S., including Thousand Oaks, Simi Valley, Newbury Park, and Moorpark. Overall, crime in the county is 33% lower than California and U.S. rates.

Two of the California Channel Islands are part of the county: Anacapa Island, which is the most visited island in Channel Islands National Park, and San Nicolas Island.