Diablo (Spanish for "Devil") is a census-designated place (CDP) in Contra Costa County, California, United States.

[6] According to the United States Census Bureau, the CDP has a total area of 1.4 square miles (3.6 km2), all of it land.

The racial makeup of Diablo was 1,065 (92.0%) White, 1 (0.1%) African American, 2 (0.2%) Native American, 55 (4.7%) Asian, 0 (0.0%) Pacific Islander, 5 (0.4%) from other races, and 30 (2.6%) from two or more races.

There were 439 housing units at an average density of 323.4 per square mile (124.9/km2),of which 412 were occupied, 380 (92.2%) by the owners and 32 (7.8%) by renters.

1,033 people (89.2% of the population) lived in owner-occupied housing units and 69 people (6.0%) lived in rental housing units.

There were 348 housing units at an average density of 357.0 per square mile (137.8/km2).

[9] In terms of real estate prices, Forbes magazine rated Diablo the fourth most expensive ZIP code in the United States.

Of the 341 households 37.8% had children under the age of 18 living with them, 85.3% were married couples living together, 3.5% had a female householder with no husband present, and 9.4% were non-families.