Newcastle House is a fine country house located about 6 km from the town of Ballymahon, and close to the R 392, the road from Mullingar to Ballymahon.
After recent architectural appraisal, the oldest section of the house has been dated to about 1730, though the site has been inhabited probably since the medieval period. The family that owned Newcastle for the greater part of its history was the Harmans, later King-Harmans.
It has been suggested that the oldest part of Newcastle House dates from the later part of the 1600s when Robert Choppin or Chopayne owned the estate.
The Harman family’s association with it was the result of the marriage of Frances Sheppard, heiress of Newcastle, to Wentworth Harman in the 1690s. Wentworth’s daughter, Anne married as his second wife Sir Laurence Parsons of Birr Castle, King’s County (Offaly).
Their son, Laurence Parsons-Harman (1749-1807) of Newcastle House, served as an M.P. and was created Lord Oxmantown in 1792, and Earl of Rosse in 1806. He is credited with significant changes to the house, including the construction of the side wings which have fine ceiling plasterwork and Adams-style Neo-Classical fireplaces.
In 1772, Laurence married Lady Jane King, who is still referred to in Longford lore as ‘Lady Rosse’. She was a staunch member of the Church of Ireland and contributed to the construction and maintenance of churches and schools on the estate.
Her grandson was the formidable Laurence, who assumed the additional name ‘Harman’, becoming Laurence Harman King-Harman. He ran the estate for about thirty-five years until his death in 1875. The clock tower in Kenagh commemorates him (entry on King-Harman Memorial Clock Tower).
The King-Harman estate reached its greatest extent in the latter years of the 19th century, comprising almost 29, 000 acres in 1876. The lands were spread across south Longford and over the border into Westmeath, and there were small pockets in north Longford too.
The family also had lands in Co. Roscommon, where their seat was Rockingham, near Boyle. The Land Acts facilitated tenants in purchasing their farms in the early 20th century and Newcastle declined rapidly thereafter.
The last resident King-Harman, Col. Wentworth Alexander, died in 1949 and the house and remaining land were sold in 1951. Since then Newcastle has been a convent boarding school, a private residence, a hotel and a guest house.