Dillon Beach is a census-designated place in Marin County, California, United States. Dillon Beach is located 3.25 miles west of Tomales, at an elevation of 89 feet. The population was 283 at the 2010 census. Dillon Beach was named after the founder, George Dillon, who settled there in 1858. The area includes a public access beach, as well as a private beach resort, the only private beach in California.