Jackson, Henry (1750?–1817), iron founder and United Irishman, was the fourth son in the family of five sons and one daughter of Hugh Jackson (1710?–77) of Creeve, Co. Monaghan, and his wife, Eleanor (née Gault), who belonged to a family engaged in the linen trade, apparently nearby at Carrickmacross. Hugh Jackson introduced the linen trade to Ballybay, Co. Monaghan, and generally improved the town. Henry Jackson, by his own account, started in business as an ironmonger in 1766. He is listed in the Dublin Directory from 1768 as an ironmonger in Pill Lane, and from 1787 as also an iron founder or iron and brass founder in Old Church Street. By 1779 he was sufficiently affluent to be a subscriber to the General Insurance Company of Ireland. In 1798 he had, besides a foundry in Church Street (‘wrought by a steam engine, the first ever erected in Dublin’, according to Jackson himself), mills for rolling and slitting iron on the quays and for grinding corn in Phoenix Street (both also steam powered) and iron mills at Clonskeagh.
Jackson's involvement in Dublin politics can be dated from 1786, when he joined James Napper Tandy (qv) on the common council as a representative of the merchants’ guild. Under the influence of the French revolution, he associated with Tandy, Archibald Hamilton Rowan (qv), and Oliver Bond (qv) in forming an independent battalion of Volunteers, known as ‘national guards’, who wore sans-culotte trousers and had caps of liberty on their coat buttons (1792). Jackson was a member of the Dublin Society of United Irishmen, probably from its inception (November 1791), sat on several of its committees, acted as its secretary and later as its treasurer, and was present at what proved to be the final meeting of the society when it was raided by the police (23 May 1794). To display his sympathies he named his country house near Dublin ‘Fort Paine’ (Drennan–McTier letters, ii, 160). He was one of the liberal group on the common council who, in March 1795, opposed the recall of Earl Fitzwilliam (qv), but by the end of the year his membership had ceased and he was with those radical United Irishmen who contemplated and later planned insurrection, his house in Pill Lane sometimes being used for meetings. He was said in 1797 to be making cannon balls that met French artillery specifications. A member of the United Irish national directory, Jackson liaised with a delegation from the United Britons in Dublin carrying an address from the London Corresponding Society (January 1798). He was arrested on 12 March 1798, not, like other members, at the house of Bond, who was his son-in-law, but elsewhere in Dublin.
Banished under 38 Geo. III, c. 78, Jackson managed, with the support of the American consul, to get permission to enter the United States in order to set up an iron foundry (1799). His iron business in Dublin continued to flourish, managed at first by his son Hugh (also arrested in 1798), who seems to have followed him to America in 1803, and then by his daughter Eleanor Bond (d. 1843) and other relatives. Jackson settled at first in Pennsylvania and bought some land, but then moved to Baltimore in Maryland. His wife, Elizabeth, the sister of Foliot Magrath (1769?–1821), a Dublin merchant, died at Baltimore on 12 August 1805. Eleanor Bond seems to have joined her father, as she accompanied him on a visit to England (1810), and died at Baltimore. According to Madden, Henry Jackson spent his last years in New York and died there on 4 July 1817, supposedly aged sixty-four; he was in fact somewhat older.
Three of Jackson's brothers were living in Co. Monaghan in 1798 and had United Irish sympathies: James (1743?–1822), probably a linen draper; John (1744–1824), a linen bleacher; and Hugh (d. 1810), an apothecary, who seems to have been implicated in the rebellion and whose daughter Ellen (d. 1800?) married William Tennent (qv). The Jackson family was presbyterian: John Jackson was an elder of First Ballybay congregation.