<page_title> List of the most populous counties in the United States </page_title> <section_title> List </section_title> <table> <cell> California <col_header> State </col_header> </cell> <cell> California <col_header> State </col_header> </cell> <cell> California <col_header> State </col_header> </cell> <cell> Riverside <col_header> County </col_header> </cell> <cell> California <col_header> State </col_header> </cell> <cell> 2,189,641 <col_header> April 1, 2010 census </col_header> </cell> </table>
As of the 2010 census, the population of Riverside County was 2,189,641, making it the 4th-most populous county in California in the United States.