Byron is a census-designated place (CDP) in Contra Costa County, California, United States. The population was 1,277 at the 2010 census.
According to the United States Census Bureau, the CDP has a total area of 6.5 square miles (16.8 km²), all of it land. It is located 5.5 miles (9 km) southeast of Brentwood.
Byron's first post office opened in 1878. Byron is named after an employee of the railroad.