Good Americans, when they die, go to Paris.

On another vacation in the 1840s Appleton met Horace Mann and took him dancing at the Champs-Élysées in Paris. Appleton befriended the poet and professor Henry Wadsworth Longfellow during a trip to Europe in the 1830s; the two became close friends. In April 1884 while in New York Appleton developed pneumonia.

Henry Wadsworth Longfellow was his brother-in-law after he married Appleton's sister Frances.