Multnomah County is one of 36 counties in the U.S. state of Oregon. Though smallest in area, it is the most populous as its county seat, Portland, is the state's largest city. The county is likely named after Native American people first recorded in the journals of the Lewis and Clark Expedition, Mulknomans, who lived in a village on the east side of present-day Sauvie Island. In 2000, the county's population was 660,486. Multnomah County apartments for rent comparison page shows most up to date rent information on Multnomah County apartments and houses. Rent information is obtained from multiple rental sources but we cannot guarantee their accuracy.