Bellingham, Thomas (1644/5–1721), army officer and landowner, was the son of Henry Bellingham (qv) (d. 1676) and his wife, Lucy, daughter of another Louth gentleman, William Sibthorpe of Dunany. Henry Bellingham was a cornet in the Cromwellian army, who acquired in the 1650s an estate of c.706 hectares at Gernonstown, Co. Louth; he was MP for Co. Louth after the restoration, and his ownership of his property was confirmed in 1666. Thomas Bellingham, born in Dublin, was educated at St Patrick's cathedral school before entering TCD, aged fifteen, on 16 February 1660. He married, in 1671, Abigail (‘Nabby’), daughter of William Handcock of Twyford, Co. Westmeath, where their only son, Henry, was born (1675).
Thomas inherited his father's property, his enjoyment of which, however, was interrupted by the accession of James II (qv) (1685) and the disruption that followed. Like many protestant gentlemen, he fled to England, spending his time at Preston, near his English second cousins. In May 1690 he returned to Ireland as a colonel in the Williamite army. His knowledge of the countryside north of the River Boyne enabled him to act as aide to William III (qv) before the famous battle, at which both men were present. He kept a campaign diary for the period 28 August 1689 to 12 September 1690, which was edited and published by Anthony Hewitson as Diary of Thomas Bellingham, an officer under William III (1908). The diary reveals a deep concern for religious matters as well as the writer's enjoyment of rural pastimes. By a warrant signed by William III at Finglas shortly after the battle, Bellingham was appointed high sheriff of Co. Louth, an office he had already held (1683–4); he was also MP for Co. Louth (1692–3, 1695–9, 1703–13). In the 1690s, Bellingham built, in the Dutch style, a new house (to replace one burned down by the Jacobite army) and planted many trees, making Gernonstown (renamed Castlebellingham after 1700) the ‘delightful spot’ visited in 1744 by Isaac Butler (qv). Thomas Bellingham died on 15 September 1721. His portrait was painted by Jervas; his diary is now in the RIA. His only son, Henry (born 1676), was MP for Dundalk (1703–14) and a whig; he died on 15 March 1741.