- Total 7,303 sq mi (18,910 km2)
- Land 7,206 sq mi (18,660 km2)
- Water 97 sq mi (250 km2)
Highest elevation 10,843 ft (3,305 m)
Lowest elevation −234 ft (−71 m)
Population (April 1, 2010)
- Total 2,189,641
- Estimate (2016) 2,387,741
- Density 300/sq mi (120/km2)
The indigenous peoples of what is now Riverside County are the Luiseño, Cupeño and Cahuilla Indians. The Luiseño lived in the Aguanga and Temecula Basins, Elsinore Trough and eastern Santa Ana Mountains and southward into San Diego County. The Cahullia lived to the east and north of the Luiseño in the inland valleys, in the Santa Rosa and San Jacinto Mountains and the desert of the Salton Sink.
The first European settlement in the county was a Mission San Luis Rey de Francia estancia or farm, at the Luiseño village of Temecula. Grain and grapes were grown here. In 1819, the Mission granted land to Leandro Serrano, mayordomo of San Antonio de Pala Asistencia for the Mission of San Luis Rey for Rancho Temescal.
Following Mexican independence and the 1833 confiscation of Mission lands, more ranchos were granted. Rancho Jurupa in 1838, El Rincon in 1839, Rancho San Jacinto Viejo in 1842, Rancho San Jacinto y San Gorgonio in 1843, Ranchos La Laguna, Pauba, Temecula in 1844, Ranchos Little Temecula, Potreros de San Juan Capistrano in 1845, Ranchos San Jacinto Sobrante, La Sierra (Sepulveda), La Sierra (Yorba), Santa Rosa and San Jacinto Nuevo y Potrero in 1846.
When the initial 27 California counties were established in 1850 the area today known as Riverside County was divided between Los Angeles County and San Diego County. In 1853 the eastern part of Los Angeles County was used to create San Bernardino County. Between 1891 and 1893 several proposals, and legislative attempts, were put forth to form new counties in Southern California. These proposals included one for a Pomona County and one for a San Jacinto County. None of the proposals were adopted until a measure to create Riverside County was signed by Governor Henry H. Markham on March 11, 1893.
The new county was created from parts of San Bernardino County and San Diego County. On May 2, 1893, seventy percent of voters approved the formation of Riverside County. Voters chose the city of Riverside as the county seat, also by a large margin. Riverside County was officially formed on May 9, 1893, when the Board of Commissioners filed the final canvass of the votes.
The county is also the location of the March Air Reserve Base, one of the oldest airfields continuously operated by the United States military. Established as the Alessandro Flying Training Field in February 1918, it was one of thirty-two U.S. Army Air Service training camps established after the United States entry into World War I in April 1917. The airfield was renamed March Field the following month for 2d Lieutenant Peyton C. March, Jr., the recently deceased son of then-Army Chief of Staff, General Peyton C. March, who was killed in an air crash in Texas just fifteen days after being commissioned. March Field remained an active Army Air Service, then U.S. Army Air Corps installation throughout the interwar period, later becoming a major installation of the U.S. Army Air Forces during World War II. Renamed March Air Force Base in 1947 following the establishment of the U.S. Air Force, it was a major Strategic Air Command (SAC) installation throughout the Cold War. In 1996, it was transferred to the Air Force Reserve Command and gained its current name as a major base for the Air Force Reserve and the California Air National Guard.
Riverside county was a major focal point of the Civil Rights Movements in the US, especially the African-American sections of Riverside and heavily Mexican-American communities of the Coachella Valley visited by Cesar Chavez of the farm labor union struggle.
Riverside county has also been a focus of modern Native American Gaming enterprises. In the early 1980s, the county government attempted to shut down small bingo halls operated by the Morongo Band of Cahuilla Mission Indians and the Cabazon Band of Mission Indians. The tribes joined forces and fought the county all the way to the U.S. Supreme Court, which ruled in the tribes’ favor on February 25, 1987. In turn, Congress enacted the Indian Gaming Regulatory Act in 1988 to establish a legal framework for the relationship between Indian gaming and state governments. Naturally, both tribes now operate large casinos in the county: the Morongo Casino, Resort & Spa and the Fantasy Springs Resort Casino adjacent to Spotlight 29 Casino.
The county’s population surpassed one million people in 1980 when the current trend of high population growth as a major real estate destination began in the 1970s. Once strictly a place for long distance commuters to L.A. and later Orange County, the county and city of Riverside has become more of a place to establish new or relocated offices, corporations and finance centers in the late 1990s and 2000s. More light industry, manufacturing and truck distribution centers became major regional employers in the county.