Byron, California is located in Contra Costa County. Below is a market update video for Contra Costa County. For detailed market report of your neighborhood, please contact us. Byron is a census designated place (CDP) in Contra Costa County, California, United States. The population was 1,277 at the 2010 census. Byron's first post office opened in 1878. Byron is named after an employee of the railroad. This region experiences warm (but not hot) and dry summers, with no average monthly temperatures above 71.6 °F. Byron is windy, and dust devils sometimes appear. According to the Köppen Climate Classification system, Byron has a warm-summer Mediterranean climate, abbreviated "Csb" on climate maps.