Riverside is a city in and the county seat of Riverside County, California, United States. It is named for its location beside the Santa Ana River…Riverside is a city in and the county seat of Riverside County, California, United States. It is named for its location beside the Santa Ana River. It had a population of 314,998 as of the 2020 census. It is the most populous city in the Inland Empire metropolitan area and Riverside County, the 12th-most populous city in California, and the 59th-most populous city in the United States. Along with San Bernardino, Riverside is a principal city in the nation's 13th-largest metropolitan statistical area; the Riverside–San Bernardino–Ontario had 4.6 million residents in 2020. Riverside is about 50 miles southeast of downtown Los Angeles and is also part of the Greater Los Angeles area.