Documents from the Letters and Papers of William H. Herndon:
regarding Nancy Hanks, mother of Abraham Lincoln
Mrs. Thomas Lincoln's Statement
Monograph on Nancy Hanks by William Herndon
Note that since we put this web page up, a new version of Herndon's Informants has been published on-line. Much more Lincoln related correspondence can be found there including a letter from Charlotte Vawter that appears to be the origin of the "Shipley theory" and a version of the Verduin hypothesis.
In addition (not from Herndon's Informant):