Rio Oso is a census-designated place (CDP) in Sutter County, California. Rio Oso sits at an elevation of 52 feet (16 m). The ZIP Code is 95674. The community is inside area code 530. The 2010 United States census reported Rio Oso's population was 356.
According to the United States Census Bureau, the CDP covers an area of 6.5 square miles (16.9 km²), all of it land.