The Rossmore Papers in PRONI comprise around 5200 documents and around 55 volumes, 1610 to around 1959 (though unevenly spread, and mainly around 1750-1959).
Although the papers bear the PRONI prefix 'T', which usually denotes photocopies, they are present in the original. The only exceptions are around 25 important architectural drawings, the originals of which were destroyed when Lord Rossmore's house in the demesne of Rossmore Park was burnt down by terrorists. The rest of the papers in the house would have shared the same fate, but for the very fortunate accident that they had been lent to PRONI for conservation and photocopying (which is why they were given a 'T' number). Following the destruction of his house, Lord Rossmore generously decided that his best course of action was to allow the originals to remain with PRONI. This deposit of 1972-1973 consisted of personal and political papers which came originally from Rossmore Park. It was followed, nearly 25 years later, by a further deposit from the office of Messrs Martin & Brett, Mill Street, Monaghan, solicitors (and former tenants) to successive Lords Rossmore. This latter deposit of estate office-type material, from 1703 onwards, is in the main rather late and disappointing: that from Rossmore Park, though very largely 19th century and therefore late, is far from disappointing.
One important adjunct to, or rather stray from, the archive, is a volume of maps in the private possession of Mr and Mrs Christopher Pringle, Glenview, Monaghan. The surveyor was Arthur Richards Neville, and the maps reveal that in 1790 the estate comprised 83 townlands and over 8300 Irish acres (equivalent to 11,960 statute acres), all in the barony of Monaghan, Co. Monaghan, and mostly centring on the county town of Monaghan itself. The volume has been microfilmed by PRONI under reference number MIC624. The list of the rentals section of the archive, T2929/38, sets out how - from around 1892 onwards - the estate was arranged and managed, and what were its component townlands and streets in the town of Monaghan.