Sources: IU-R
- Samuel L. Clemens to Benjamin P. Shillaber, 28 May 1870 · Buffalo, N.Y · UCCL00470
- Samuel L. Clemens to Unidentified, 6 January 1871 · Buffalo, N.Y · UCCL11886
- Samuel L. Clemens to George Bentley per Fanny C. Hesse, 5 December 1876 · Hartford, Conn · UCCL12341
- Samuel L. Clemens to George Bentley, per Fanny C. Hesse, 12 February 1877 · Hartford, Conn · UCCL12342
- Samuel L. Clemens to George Bentley, 3 August 1877 · Elmira, N.Y · UCCL12343
- Samuel L. Clemens to Chatto and Windus, 1 December 1880 · Hartford, Conn · UCCL01863
- SLC to James R. Osgood, 3 June 1881 · Hartford, Conn · UCCL01968
- SLC to Unidentified, 23 November 1888 · Hartford, Conn · UCCL03836
- SLC to Chatto & Windus, 22 July–24 July 1897 · Weggis, Switzerland · UCCL08644
- SLC to Katie Leary, February 1898 · Unknown place · UCCL11499
- SLC to J. Henry Harper, 8 February 1898 · Vienna, Austria · UCCL05345
- SLC to Mollie Clemens, 24 May 1898 · Kaltenleutgeben, Austria · UCCL05392
- SLC to Unidentified, 10 November 1898 · Vienna, Austria · UCCL05464
- SLC to Unidentified, 11 February 1899 · Vienna, Austria · UCCL05545
- SLC to Susannah Isabella S. (Susan Belle) Bohon, 20 July 1904 · Lee, Mass · UCCL06894
- SLC to Unidentified, 6 December 1905 · New York, N.Y · UCCL12370
- SLC to Eulabee Dix, 23 January 1908 · New York, N.Y · UCCL09381
- SLC to William D. Howells, 18 January 1909 · Redding, Conn · UCCL08315
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