Approximately half of all United States presidents can trace at least one lineage back to the island of Ireland, but a notable subset of 16 former commanders-in-chief have ancestral ties specifically to the north-east - modern-day Northern Ireland - according to the Irish Family History Centre.

Fiona Fitzsimons, director of the centre based at Dublin's EPIC museum, has researched the family histories of several presidents. Her work highlights a pattern of Scots-Irish or Ulster-Scots heritage, predominantly Presbyterian, though some presidents, like Richard Nixon and Gerald Ford, shared Irish Quaker ancestry. While Nixon's maternal line came from County Kildare, Ford's roots in Ulster were more extensive: his fifth-great-grandfather John Blackburn III lived in Loughgall, County Armagh, and the family also had connections to the neighbouring townland of Creenagh and to Donaghcloney in County Down.

Andrew Jackson, the seventh president, is perhaps the earliest example. His parents and older brothers emigrated from Carrickfergus, County Antrim, two years before his birth in 1767. Jackson's Presbyterian family was typical of the Ulster-Scots migration that shaped much of early America. He served two terms and founded the Democratic Party, though his legacy also includes controversial policies on slavery and Native American displacement.

More recent presidents with confirmed Northern Ireland ancestry include George H.W. Bush. His fourth great-grandfather, William Holliday, left Rathfriland, County Down, for Kentucky over 200 years ago. Former president Jimmy Carter, too, had ancestors from County Antrim, according to Fitzsimons' research. Harry Truman, Theodore Roosevelt, and Woodrow Wilson are also among the 16.

The genealogist has presented personal family histories to sitting presidents, including Joe Biden in 2016, though Biden's own Irish roots are in County Mayo and County Louth rather than the north. Of all Irish-American presidents, Fitzsimons considers John F. Kennedy the most engaged with his heritage; he maintained contact with relatives in County Wexford and visited them before and during his presidency.

Despite the deep-rooted connections, Professor Liam Kennedy of the Clinton Institute for American Studies observes that the political influence of Irish-America has waned. He described the era of presidential homecomings to Ireland as outdated and noted the absence of a cohesive Irish voting bloc, with the community now assimilated and politically diverse. He suggests the transformation, rather than disappearance, of Irish-American identity means ancestral ties play a diminished role in electoral politics.