Dear Neven Kliček:
Thank you for posting your question on History Hub!
The Manuscript Division of the Library of Congress collects, arranges, and makes accessible personal and organizational records relating to American history. You can view collections held by the Manuscript Division that have been digitized online here, and collections from other divisions in the Library that have been digitized here. Should you have any questions about digital materials at the Library, you can contact staff via Ask a Librarian.
Best wishes in your research!
Library of Congress
Dear Mr. Kliček,
Thank you for posting your request on History Hub!
We searched the National Archives Catalog for “Correspondence” and located 13,724 archival descriptions with digital objects from 1860 to 1909. Since all are digitized, they are available using the Catalog. Some have been transcribed but most have not.
We hope this is helpful. Best of luck with your research!