DempseyIrish Anglicized form of Irish Ó Díomasaigh meaning "descendant of Díomasach", a given name meaning "proud".
DouglasScottish Anglicized form of Gaelic Dubhghlas, which meant "dark river" from dubh "dark" and glais "water, river" (an archaic word related to glas "grey, green"). This is the name of various places in Scotland, such as a tributary of the River Clyde.
DoyleIrish From the Irish Ó Dubhghaill, which means "descendant of Dubhghall". A famous bearer was Sir Arthur Conan Doyle (1859-1930), the author of the Sherlock Holmes mystery stories.