A commentator made the suggestion to search in books here in the Brigham Young University Library. So, since I am writing this in the Library this evening, I took time to go to the section with books of quotes. I looked through about ten of them. Including these two very comprehensive books:
Bartlett, John, and Justin Kaplan. Familiar Quotations: A Collection of Passages, Phrases, and Proverbs Traced to Their Sources in Ancient and Modern Literature. Boston: Little, Brown, 2002.
Partington, Angela. The Oxford Dictionary of Quotations. Oxford: Oxford university press, 1996.
Not only was there no reference in the section of each for Longfellow, the quote itself was not in any of the books I looked at.
At this point, my search is over. As far as I am concerned, the statement is a modern one attributed to Longfellow with no real connection whatsoever.
Now, this should be an important lesson for every researcher, genealogical or otherwise, check your original sources. You just may find that a widely accepted fact is actually false.