Much of Greeley's correspondence was destroyed by fire after his death, but a considerable body of material remains. The principal collections, indispensable for a study of the man and his career, are the Greeley Papers in the New York Public Library, the Greeley Papers in the Library of Congress, the Greeley Letters in the library of the New-York Historical Society, and the Henry A. Stahl Collection of Greeley letters, now in the possession of Mr. Edward C. M. Stahl at Chappaqua, New York. Of these, the letters in the New York Public Library are the most important, those of Greeley to Schuyler Colfax being particularly informative. The Library of Congress collection contains numerous letters and transcripts of letters to and from Tribune associates (especially Charles A. Dana), and other acquaintances and friends. The New-York Historical Society collection is smaller, but important for special periods. The Stahi Collection consists chiefiy of letter books, and copies of Greeley's letters are always suspect, because of his unique handwriting. But it also contains other letters than those of Greeley, some of which are not available elsewhere, and so cannot be ignored.
Other Greeley letters are scattered throughout the country, in a wide variety of collections. The most important of these are the Rufus W. Griswold Papers in the Boston Public Library, the Margaret Fuller Correspondence in the Harvard Library, the Salmon P. Chase Papers in the Historical Society of Pennsylvania, the Edwin D. Morgan Papers in the Albany State Library, the Mrs. H. C. Ingersoll Papers in the Library of Congress, the Gerrit Smith Papers in the Syracuse University Library, the collection of Greeleyana in the Huntington Library. There are scattered but important Greeley items in such collections as the Henry Clay Papers, the Thaddeus Stevens Papers, the Elihu B. Washburne Papers in the Library of Congress. Rhees Library at the University of Rochester has a number of Greeley letters that should not be overlooked by any student of the man. The Papers of Thurlow Weed and of William Henry Seward at the University of Rochester contain much valuable Greeley material.
A comprehensive bibliography of Greeley's writings is to be found in the Greeley Papers in the Library of Congress. Items particularly valuable for a study of Greeley's policies and ideas are his editorials (as cited in the text) in the Continental Monthly, the Independent, the Jeffersonian, the Log Cabin, the New-Yorker, the New York Tribune.
Particularly valuable sources for printed letters are:
J. Benton (ed.), Greeley on Lincoln: with Mr. Greeley's Letters to Charles A. Dana and a Lady Friend. . . ( N. Y., 1873).
0. M. Dickerson, "Letters of Horace Greeley to Nathaniel C. Meeker," Colorado Magazine, XIX ( March 1942), 50-62, and XIX ( May 1942), 102-10.