Ó Tighearnaigh of Cenél nEógain

This family lived in the territory of Fearnmuigh or Fearnmaigh [which means 'the territory of the plain'], in an area in South Monaghan/South Armagh that is the present Barony of Farney, whose principal town is Carrickmacross.^[2]

Ó Tighearnaigh of Uí Fiachrach Muaidhe

This family were Lords of Carra. Almost the only family member recorded in the annals was Flann Ó Tighearnaigh. Gilbert Ó Tigernaig, Bishop of Annaghdown (1306–1323), was also a member of this family.

Ó Tighearnaigh of Brega

This family claimed descent from Tigernach mac Fócartai (died 865), one of the Kings of Brega. They were a branch of the southern Uí Néill. "The Kingdom is said to have stretched from Birr in County Offaly to the Hill of Uishneach in Westmeath. Tighearnach resided at the Great Crannóg of Lagore, which is situated near Ratoath in County Meath, not far from Dublin. Tighearnach led the Irish to a great victory over the Norse Vikings in 848 A.D."^[2]

Ó Tighearnaigh of Ormond

A family of the name resided in Ormond, now County Tipperary. Their origins are obscure.^[2] New research now confirms that this family was indeed an indigenous sept. Their seat was in the townland of Park and their lands, Fearann Ó Tighearnaigh, took in most of the present-day townlands of Ballymackey, Ballyknockane, Carrowea, Clash, Falleen, Gortnadrumman, Kilgorteen and Knockane.

Ó Tighearnaigh of Corcu Modruad

This is an area in northern County Clare. This sept were hereditary priests and monks.

In arts and media

• Brian Tierney (medievalist) (1922–2019), historian and medievalist
• Mark Aloysius Tierney (1795–1862), English Catholic historian
• Patrick Lennox Tierney (1914–2015), art historian, specialist on Japan
• Tom Tierney (artist) (1928–2014), American paper doll artist

Government, law, and politics

• Darren Tierney, British civil servant, Director General for Propriety and Ethics
• Frank A. Tierney, Deputy Commissioner under the Workmen's Compensation act
• Gayle Tierney, Australian politician, Labor party
• George Tierney (1761–1830), English Whig politician
• James Tierney (politician) (born 1947), Attorney General of Maine
• John Tierney (Australian politician) (born 1946), Liberal senator
• John Tierney (Irish politician) (born 1951)
• John F. Tierney (born 1951), United States Representative from Massachusetts
• John H. Tierney (1832–1907), American politician and farmer
• John J. Tierney (1926–2005), American Boston city council member
• Joseph M. Tierney (1941–2009), American politician, father of Maura Tierney
• Michael Tierney (politician) (1894–1975), professor at University College Dublin
• Patrick Tierney (Irish politician) (1904–1990), Irish Labour party politician
• Peter Tierney Murrell (born 1964), CEO of the Scottish National Party
• Susan Tierney (born 1951), American academic and Government policy administrator
• Sydney Tierney (1923–2010), British Labour Party politician
• Thomas Tierney (1916–1998), Irish mayor of Galway, Ireland
• Thomas M. Tierney (1919–2001), American administrator of the Bureau of Health Insurance
• Tim Tierney (born 1974), Canadian councillor and politician
• William Tierney Robarts (1786–1820), British politician and businessman
• William L. Tierney (1876–1958), Democratic member of the US House of Representatives

In sport

In business

• Brian Tierney (born 1957), American businessman and newspaper publisher
• Michael Tierney (born 1989), American businessman, founder of Stuffed Puffs
• Paul E. Tierney (born 1943), American business professor and venture capitalist
• Thomas J. Tierney (born 1954), business executive, chairman of eBay

In education

• Alison J. Tierney (born 1948), British nursing theorist and researcher
• Charles Rust-Tierney (born 1955), American ACLU chapter president
• James Tierney (politician) (born 1947), Attorney General of Maine
• Keith Tierney, Canadian scientist and academic
• Myles Tierney (1937–2017), American mathematician and professor
• Robert J. Tierney, Dean Emeritus at the University of British Columbia
• T. F. Tierney (born 1951), American urbanist, network theorist and educator
• William G. Tierney, American scholar in higher education and author

In religion

• Cornelius Tierney (1872–1931), Irish priest and missionary
• Gilbert Ó Tigernaig, bishop of Annaghdown
• Michael Tierney (bishop) (1839–1908), Roman Catholic bishop
• Tigernach of Clones (died 549), Irish saint, patron
• Tigernach Ua Braín (died 1088), Abbott of Clonmacnoise

In science

• James Edward Tierney Aitchison (1835–1898), Scottish surgeon and botanist
• Jessica Tierney (born 1982), American paleoclimatologist
• Luke Tierney, American statistician and computer scientist
• Matthew John Tierney (1776–1845), Irish surgeon and royal physician

In other fields

• Emiko Ohnuki-Tierney (born 1934), Japanese-American anthropologist
• Flann Ó Tighearnaigh (died 1273), Gaelic Irish lord
• Paul Tierney (referee) (born 1980), English football referee
• Tigernach mac Fócartai (died 865), king of Lagore
• William Tierney Clark (1783–1852), English civil engineer of bridges