Sources: NSyU
- Samuel L. Clemens to Schuyler Colfax, 10 or 11 December 1869 · New York, N.Y · UCCL00384
- SLC to Karl and Hattie J. Gerhardt, 25 February–27 February 1881 · Hartford, Conn · UCCL12017
- SLC to Richard Watson Gilder, 21 May 1887 · Unknown place · UCCL03576
- SLC to John C. Kinney, 3 June 1889 · Hartford, Conn · UCCL03899
- SLC to Chatto & Windus, 22 November 1891 · Berlin, Germany · UCCL04255
- SLC to Robert U. Johnson, 5and 6 July 1895 · Elmira, N.Y · UCCL04926
- SLC to Charles Lancaster, 7 July 1897 · London, England · UCCL09349
- SLC to Francis E. Bliss, 10 December 1898 · Vienna, Austria · UCCL05478
- SLC to L. M. Powers, 24 February 1902 · Riverdale, N.Y · UCCL06283
- SLC to Frederick A. Duneka, 26 April 1903 · Riverdale, N.Y · UCCL06632
- SLC to Isabel V. Lyon, 14 June 1906 · Dublin, N.H · UCCL11110
- SLC to Charlotte Teller, 14 June 1906 · Dublin, N.H · UCCL07469
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