<page_title> Washington County, Oregon </page_title> <section_title> Demographics </section_title> <table> <cell> 2010 <col_header> Historical population </col_header> <col_header> Census </col_header> </cell> <cell> 529,710 <col_header> Historical population </col_header> <col_header> Pop. </col_header> </cell> </table>
As of the 2010 census, the population was 529,710, making Washington County the second populous county.