The manuscripts consist of a small number of documents of the 13th to 17th centuries and an extensive collection of eighteenth century papers, including the private and official correspondence of the Howard family with most of the important men of the period. Among the public documents are papers and minutes relating to the "American War of Independence, the negotiations with the Americans in 1778-80 [and] the fifth Earl of Carlisle's mission to America as British commissioner". Of the private correspondence the largest group contains the letters of George Selwyn to the fifth Earl of Carlisle, 1767-1790.

The manuscripts consists of charters and other documents of the Douglas family; papers of the first Duke of Queensberry as commissioner to the Pariliament of Scotland 1685; letters to him from James II, John Graham of Claverhouse, the third Duke of Hamilton, the fifth Earl of Moray, and the first Earl of Melfort.