Clapp, Ebenezer. The Clapp Memorial: Record of the Clapp Family in America, Containing Sketches of the Original Six Emigrants and a Genealogy of their Descendants Bearing the Name. With a Supplement and the Proceedings at Two Family Meetings.. Boston: David Clapp & Son, 1876.
"Died in Bowery Lodgings: Sad Ending of the Career of George G. Clapp." New York Times, April 10, 1893, 3.
Allen, Gay Wilson. The Solitary Singer: A Critical Biography of Walt Whitman. New York: MacMillan, 1955.
Whitman, Walt. "Letter to William D. O'Connor, September 15, 1867." Walt Whitman: The Correspondance 1, (1961): 338-340.
The Vault at Pfaff's