Sources: NN5
- Samuel L. Clemens to Frank Fuller, 24 November 1867 · Washington, D.C · UCCL00158 NN5
- Samuel L. Clemens to Frank Fuller, 13 December 1867 · Washington, D.C · UCCL00173 NN5
- Samuel L. Clemens to Emily A Severance, 24 December 1867 · Washington, D.C · UCCL02780 NN5, OClWHi
- Samuel L. Clemens to Joseph H. Twichell, 3 January 1871 · Buffalo, N.Y · UCCL00554 NN5
- Samuel L. Clemens to Bret Harte, 7 June–28 September 1871 · Elmira, N.Y · UCCL11811 NN5, CU-MARK
- Samuel L. Clemens to Samuel S. Cox, 4 February 1874 · Hartford, Conn · UCCL01046 NN5
- Samuel L. Clemens to Samuel S. Cox, 8 February 1875 · Hartford, Conn · UCCL01190 NN5, CU-MARK
- Samuel L. Clemens to Dean Sage, 22 April 1875 · Hartford, Conn · UCCL01221 NN5
- Samuel L. Clemens to Thomas Bailey Aldrich, 28 January 1876 · Hartford, Conn · UCCL01303 NN5
- Samuel L. Clemens to Frank Fuller, 26 November 1879 · Hartford, Conn · UCCL01747 NN5
- Augustus Saint-Gaudens to SLC, 2 August 1882 · UCLC41193 NN5
- SLC to Karl Gerhardt and Hattie J. Gerhardt, 4 August 1882 · Elmira, N.Y · UCCL02259 NN5, MB
- SLC to Samuel S. Cox, 9 July 1887 · Elmira, N.Y · UCCL03598 NN5
- SLC to Caroline B. Le Row, 4 November 1888 · Hartford, Conn · UCCL03827 NN5
- SLC to Douglas Taylor, 21 October 1889 · Hartford, Conn · UCCL03956 NN5
- SLC to Frederick J. Hall, 25–27 February 1893 · Florence, Italy · UCCL04633 NN-BGC, NN5
- SLC to Webster (C. L.) & Co., 8 March 1893 · Florence, Italy · UCCL12383 NN5
- SLC to Webster (C. L.) & Co., 16 August 1893 · Krankenheil, Germany · UCCL04435 NN5
- SLC to OLC, 12 January 1894 · New York, N.Y · UCCL04671 CU-MARK, NN5
- SLC to Henry Gilsey, 7 August 1894 · New York, N.Y · UCCL04774 NN5
- SLC to Heinrich Obersteiner, 5 October 1897 · Vienna, Austria · UCCL05294 NN5
- SLC to John Brisben Walker, 19 September 1898 · Kaltenleutgeben, Austria · UCCL05435 NN5
- SLC to H. F. Russell, 24 June 1899 · London, England · UCCL05643 NN5
- SLC to Mrs. T. Douglas Murray, 14 August 1900 · London, England · UCCL05851 NN5
- SLC to Laura F. McQuiston, 11 April 1901 · New York, N.Y · UCCL06033 NN5
- SLC to Mrs. Henry Satterlee Fitch, 25 October 1901 · Riverdale, N.Y · UCCL06165 NN5
- SLC to Isabel V. Lyon, 25 September 1906 · New York, N.Y · UCCL07476 NN5
- SLC per Isabel V. Lyon to Frank C. Lascelles, 19 January 1909 · Redding, Conn · UCCL08336 NN5
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