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. The county is also included in the Los Angeles–Long Beach Combined Statistical Area.
Roughly rectangular, Riverside County covers 7,208 square miles (18,670 km2) in Southern California, spanning from the greater Los Angeles area to the Arizona border. Geographically, the county is mostly desert in the central and eastern portions, but has a Mediterranean climate in the western portion. Most of Joshua Tree National Park is located in the county. The resort cities of Palm Springs, Palm Desert, Indian Wells, La Quinta, Rancho Mirage, and Desert Hot Springs are all located in the Coachella Valley region of central Riverside County.
Between 2007 and 2011, large numbers of Los Angeles-area workers moved to the county to take advantage of more affordable housing. Along with neighboring San Bernardino County, it was one of the fastest-growing regions in the state prior to the recent changes in the regional economy. In addition, smaller, but significant, numbers of people have been moving into southwest Riverside County from the San Diego metropolitan area. The cities of Temecula and Murrieta accounted for 20% of the increase in population of the county between 2000 and 2007.