Although the Manuscript Reading Room has a mandate to collect only materials with a connection to the United States, there are manuscript collections in the Manuscript Reading Room that are also related to Denmark. A handful of them will be discussed here, but more can be found with the following technique. To search for Danish materials in the Manuscript Reading Room, go to Advanced Search under Search Options in the Library of Congress Online Catalog. Enter "Denmark" into the first textbox on the left, and "Danish" into the one immediately below it. Hit the OR radio button between the two textboxes. Click on the Add Limits button below, and select Manuscript from the first list, which is titled Location in the Library. Lastly, hit the Search button at the very bottom of the page.

The Manuscript Reading Room has custody of the papers of many American diplomats and others from the United States who worked in or had correspondence with individuals from Denmark, such as John Murray Forbes from when he was the American consul residing at Copenhagen and Hamburg during the years 1801-19, and Norman Hapgood from when he served as U.S. minister to Denmark in 1919.

Several important Danish Americans have deposited their archives in the Manuscript Reading Room. Jacob A. Riis, world-famous author of How the Other Half Lives, has his papers here, as has K. Aage Strand, a Danish astronomer who directed the U.S. Naval Observatory. Harald T. Friis, the radio engineer who served as a research director at Bell Labs, also left a collection with the Manuscript Reading Room.

Since the Danish West Indies became the U.S. Virgin Islands in 1917, the Manuscript Reading Room has assembled a wealth of resources pertaining to these territories. The Waldemar Westergaard Collection, 1558–1806 contains its namesake’s transcriptions of documents about the Danish West Indies, which originate in the Danish State Archives, the Royal Library of Denmark, the Municipal Archives of Copenhagen, and the Bancroft Library of the University of California, Berkeley. Records Concerning the Danish West Indies, 1776–1823 is an assortment of manuscripts and transcripts mainly concerning British naval aggression around the islands of St. Croix, St. Thomas, and St. John during the Revolutionary War. The Manuscript Reading Room will also serve, in a microfilm format, Schleswig-Holstein government records, 1619–1849. These concern trade with the Danish West Indies and the transportation of enslaved people from West Africa. (The King of Denmark ruled the partly German-speaking duchies of Schleswig and Holstein in his capacity as duke, but not as King of Denmark. This awkward arrangement led to war with the German Confederation in 1848).