"Robert Lewis," Digital Encyclopedia of George Washington (George Washington’s Mount Vernon).

Merrow Egerton Sorley, comp., Lewis of Warner Hall: The History of a Family (Baltimore: Genealogical Publishing Co., Inc., 1964), 233.

"To George Washington from Robert Lewis, 10 January 1791," Founders Online, National Archives, https://founders.archives.gov/documents/Washington/05-07-02-0120. [Original source: The Papers of George Washington, Presidential Series, vol. 7, 1 December 1790 – 21 March 1791, ed. Jack D. Warren, Jr. Charlottesville: University Press of Virginia, 1998, pp. 216–217.]

"To George Washington from Robert Lewis, 6 April 1796," Founders Online, National Archives, https://founders.archives.gov/documents/Washington/05-20-02-0014. [Original source: The Papers of George Washington, Presidential Series, vol. 20, 1 April–21 September 1796, ed. David R. Hoth and William M. Ferraro. Charlottesville: University of Virginia Press, 2019, pp. 18–20.]

"To George Washington from Robert Lewis, 26 October 1797," Founders Online, National Archives, https://founders.archives.gov/documents/Washington/06-01-02-0383. [Original source: The Papers of George Washington, Retirement Series, vol. 1, 4 March 1797 – 30 December 1797, ed. W. W. Abbot. Charlottesville: University Press of Virginia, 1998, pp. 429–430.]

"To James Madison from Robert Lewis, 8 November 1824," Founders Online, National Archives, https://founders.archives.gov/documents/Madison/04-03-02-0420. [Original source: The Papers of James Madison, Retirement Series, vol. 3, 1 March 1823 – 24 February 1826, ed. David B. Mattern, J. C. A. Stagg, Mary Parke Johnson, and Katherine E. Harbury. Charlottesville: University of Virginia Press, 2016, p. 427.]

Niles' Weekly Register (Baltimore), 24 January 1829, page 16, column 2 (Newspapers.com).

Robert Lewis at Early Colonial Settlers of Southern Maryland and Virginia’s Northern Neck Counties.

Robert Lewis at Find a Grave.

Robert Lewis at FamilySearch.