Reliez Valley is a census-designated place[2] in Contra Costa County, California.

The 2010 United States census reported Reliez Valley's population was 3,101.

According to the United States Census Bureau, the CDP has a total area of 2.363 square miles (6.120 km2), all of it land.

Reliez Valley first appeared as a census designated place in the 2010 U.S.

There were 1,300 housing units at an average density of 550.1 per square mile (212.4/km2), of which 1,244 were occupied, 1,031 (82.9%) by the owners and 213 (17.1%) by renters.