About 2,500 leases relating to the estates of the Stewart family, Marquises of Londonderry mostly for the Comber, Newtownards and Florida estates, Co. Down, but with a few for the Donegal and Derry estates, late 17th to 19th century.

Míreanna comhchosúla

• About 1000 documents, being deeds, wills, etc., relating to the estates of the Stewart family, Marquises of Londonderry, in Counties Down, Donegal and Derry, c. 1670-1850.
• About 800 maps of the estates of the Stewart family, Marquises of Londonderry, in the Comber, Newtownards and Florida areas, Co. Down, including maps by John Sloane in the 1720's, by D. Geddes in the late 18th c., plans of buildings in Newtownards, Mountstewart demesne, Strangford Lough reclamation, roads etc. 1721 - c. 1850.
• Account books, ledgers, rentals, correspondence etc. relating to the estates of the Stewart family, Marquises of London-derry, mainly in Co. Down, with rental of Comber, 1684, accounts of Strangford Lough reclamation, 19th c., Cunningburn Mill, 1808-9, 18th to 20th c.
• Papers relating to mines in the Newtownards estate of the Marquis of Londonderry, Journal of Bangor and Newtown lead mine, 1780-1782, Craiganu slate quarry, 1807-18. Inventories of furniture Mountstewart House, etc. Cotton spinner's account book, Newtownards, 1807-11.
• About 130 documents relating to the activities of Rev. Mark Cassidy, curate of Newtownards, as an advisory agent for the Marquis of Londonderry's estates in Co. Down, including references to the charity schools at Newtownards and Comber and elections, local politics, etc., 1810-39.