The small number of papers of Colonel Dennis O'Kelly (1784-c.1830) catalogued as DDLA/40 were deposited in the Brynmor Jones Library in 1974 by Joyce Elizabeth Mary, Countess Fitzwilliam (nee Langdale), as part of a larger deposit of family papers for the Langdales of Houghton Hall in the East Riding of Yorkshire.
The papers comprise some personal accounts and titles deeds. Some of the accounts relate to O'Kelly's interest in race horses, but they also include accounts with his tailor, papers to do with India bonds and a memorandum on the insuring of Lord Belfast, a debtor in the Fleet prison, to outlive his father, the marquis of Donegall, in 1794. The deeds relate to property at Stanmore in Middlesex in the late eighteenth century and include a plan of some of Nathaniel Wright's alterations in 1786. There are also deeds for property in Epsom in Surrey and in Piccadilly and Half Moon Street in London in the late eighteenth century. There are circa 70 letters to Dennis O'Kelly, about race horses, debtors and debts, dated 1785-1820, as well as three more bundles of letters dated 1794-1817 which include correspondents such as Lady Anna Donegall, Earl Moira and Arthur Wellesley.
The only marriage settlement in the collection is that of John Parkhurst and Richarda Dormer (1725). Wills in the collection are those of Andrew Dennis O'Kelly himself (1820) and John Parkhurst (1762). Miscellaneous papers in the collection include a cure for rheumatism and papers relating to Catholic affairs. DDLA/40/28 is the 1810 declaration of the Irish bishops respecting the Pope and DDLA/40/29 is a bundle of papers relating to the Prince Regent and the Princess of Wales between 1812 and 1813.