One would expect a song with a title like this to have been written by an Irish troubadour, but "When Irish Eyes Are Smiling" is actually an American song; in the words of Thomas Hischak, author of The Tin Pan Alley Song Encyclopedia
, it was "written by two of New York's most prolific professional songwriters in collaboration with a leading vaudeville performer, none of them Irish."
The most successful song with an Irish angle of the decade was published by the New York firm Witmark, copyright 1912; the credits were shared by George Graff Junior and Chauncey Olcott who wrote the words, and Ernest R. Ball, who composed the music.
Technically Hischak's claim about the song's authors is true, but to this day many Americans with even quite tenuous ancestral roots in the Emerald Isle refer to themselves or are referred to as Irish-Americans, including Presidents Ronald Reagan and Barack Obama! Although Chancellor John Olcott was American born and bred, his mother was born in Ireland and came to the United States via Canada, and Olcott himself wrote and co-wrote many Irish songs.