Riverside County is a county located in the southern portion of the U.S. state of California. As of the 2020 census, the population was 2,418,185, making it the fourth-most populous county in California and the 10th-most populous in the United States. The name was derived from the city of Riverside, which is the county seat. Riverside County is included in the Riverside-San Bernardino-Ontario Metropolitan Statistical Area, also known as the Inland Empire.