Riverside County is a county located in the southern portion of the U. As of the census , the population was 2,,, [ 3 ] [ 5 ] 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. Roughly rectangular, Riverside County covers 7, square miles 18, km 2 in Southern California , spanning from the greater Los Angeles area to the Arizona border. Geographically, the western region of the county is chaparral with a Mediterranean climate , while the central and eastern regions of the county are predominantly desert or mountainous.
Most of Joshua Tree National Park is located in the county. Between and , large numbers of Los Angeles -area workers moved to the county to take advantage of more affordable housing. In addition, smaller, but significant, numbers of people have been moving into southwest Riverside County from the San Diego metropolitan area. When Riverside County was formed in , it was named for the city of Riverside, the county seat. That city, founded in , was so named because of its location near the Santa Ana River.
In , the Mission granted Leandro Serrano permission to occupy the land for the purpose of grazing and farming, and Serrano established Rancho Temescal. The ranch was to be one of the Mission's principal rancherias , and the most distant, and it occupied most of today's San Gorgonio Pass area. Following the Mexican secularization act of by the First Mexican Republic , a series of rancho land grants were made throughout the state.
New Mexican colonists founded the town of La Placita on the east side of the Santa Ana River at the northern extremity of what is now the city of Riverside in Between and , several proposals and legislative attempts were put forth to form new counties in Southern California. None of the proposals were adopted until a measure to create Riverside County was signed by Governor Henry H. Markham on March 11, On May 2, , seventy percent of voters approved the formation of Riverside County.
