Dear Mr. Bernate,
Thank you for posting your request on History Hub!
We searched the National Archives Catalog and located Letters Received, 1789 - 1906 in the General Records of the Department of State (Record Group 59) that includes 20 items relating to Andrew Ellicott. Some of these items have been digitized and are available for viewing using the Catalog. For more information about the non-digitized records, please contact the National Archives at College Park - Textual Reference (RDT2) via email at Archives2reference@nara.gov.
Due to the COVID-19 pandemic and pursuant to guidance received from the Office of Management and Budget (OMB), NARA has adjusted its normal operations to balance the need of completing its mission-critical work while also adhering to the recommended social distancing for the safety of NARA staff. As a result of this re-prioritization of activities, you may experience a delay in receiving an initial acknowledgement as well as a substantive response to your reference request from RDT2. We apologize for this inconvenience and appreciate your understanding and patience.
Also, the Founders Online database includes 84 items authored by Andrew Ellicott and 26 items received by Ellicott. Each has been transcribed and is available for viewing. The Andrew Ellicott papers are in the custody of the Library of Congress. For more information about his papers, please contact the Library of Congress Manuscript Division using Ask a Librarian: Manuscripts.
Finally, we located the Transactions of the American Philosophical Society, Vol. 4 (1799) that includes five by Andrew Ellicott. The articles are free to view online and available to download as pdfs. The American Philosophical Society Library may have information concerning other volumes of these transactions in 1799 or the specific publication you seek.
We hope this is helpful. Best of luck with your research!
This is wonderful. I hope I may posit further questions as needed. Thank you very much.