Clarence Alfred Barnes (August 28, 1882 – May 26, 1970) was an American politician who served as Attorney General of Massachusetts from 1945 to 1949. Barnes political career began in Mansfield, Massachusetts, where he served as town counsel and moderator of the Town meeting. From 1912 to 1913, he served as a state representative, and he was a delegate to the Massachusetts Constitutional Convention of 1917–18. His son Clare Barnes, Jr. was an advertising executive who published a best-selling series of picture books.