The archive at Castle Leslie, Glaslough, Co. Monaghan, amounts to 128 PRONI boxes, plus several outsize albums, numerous rolled maps and the boxed patent of 1876 [F/2] creating the Leslie baronetcy. While the PRONI list and arrangement covers the entire archive, only a tiny fraction has in fact been copied by and is available in PRONI (MIC606 and T3827).
The material copied by PRONI is as follows:
- letters and papers, 1796 to 1819, of Charles Powell Leslie II as Colonel of the Monaghan Militia
- political - mainly Co. Monaghan election – correspondence of Charles Leslie II, 1801 to 1831
- correspondence of and between 'Minnie' Seymour and her husband, George Dawson Damer, 1820 to 1848
- letters to their daughter, Lady Constance Dawson Damer, afterwards the wife of Sir John Leslie, 1st Bt, 1854-1855, from her brother, Seymour, writing from the Crime
- letters and newspaper cuttings of Charles Powell Leslie III, 1857 to 1866, about Co. Monaghan elections, election violence in 1865
- letters to John Leslie, later Sir John, 1st Bt, 1871, about his (successful) candidature for the Co. Monaghan by-election occasioned by the death of C.P. Leslie III
- letters to Lady Constance from Sir John, March-April 1880, about his defeat at the Co. Monaghan election
- correspondence and printed matter of Sir John, October-December 1883, about the Rosslea incident
- letters to Lady Constance from the Leslies' second daughter, 'Consie', Lady Hope, 1890 to 1891, describing Viceregal life in India
- correspondence, 1894 to 1958, between Sir Shane Leslie, 3rd Bt, and his parents, grandparents, wife (Marjorie) and siblings
- correspondence, 1924 to 1972, between Sir Shane and Marjorie Leslie, on the one hand, and their children, Anita, John and Desmond, on the other (including letters to Anita from the Leslies' cousin, Clare Sheridan)
- diaries of Marjorie Leslie, 1901 to 1934 (with many gaps) and her own 'Grangerised' copies of her book, Girlhood in the Pacific, 1942
The rest – and the vast majority of - the archive is held in the National Library of Ireland.