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.

There were 140 housing units at an average density of 21.4 per square mile (8.3/km2), of which 95 (76.6%) were owner-occupied, and 29 (23.4%) were occupied by renters.

In the state legislature, Rio Oso is located in the 6th Senate District, represented by Republican Roger Niello, and in the 3rd Assembly District, represented by Republican James Gallagher.

Federally, Rio Oso is in California's 1st congressional district, represented by Republican Doug LaMalfa.