Riverside County is one of 58 counties in the U.S. state of California. The name was taken from the city of Riverside, which is the county seat. Roughly rectangle-shaped, Riverside County covers 7,208 square miles (18,670 km2) in Southern California. Riverside County lies inland ofLos Angeles County and is bordered on the west by Orange County; on the east by La Paz County, Arizona; on the southwest by San Diego County; on the southeast by Imperial County; and on the north by San Bernardino County. Together, Riverside and San Bernardino Counties have been dubbed the Inland Empire.

The population of Riverside County was 2,268,783 in 2012. It is the fourth-most populous county in California and among the fastest-growing areas of the United States in the past fifty years (since 1960). There is a high concentration of sprawling house tract communities around Riverside and along the Interstate 10, 15, and 215 freeways.

Geographically, the county is mostly desert in the central and eastern portions of the county and is a Mediterranean climate in the western portion of the county. 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 Riverside County. Large numbers of Los Angeles area workers have moved to the county in recent years[when?] to take advantage of relatively affordable[clarification needed] housing. Alongside 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-Tijuana metropolitan area. The cities of Temecula and Murrieta accounted for 20% of the increase in population of Riverside County between 2000 and 2007.