What is the origin of the last name Reilly?

The last name Reilly originated from Ireland and is an anglicized form of the Gaelic surname Ó Raghallaigh or Ó Raghallaigh, meaning "descendant of Raghallach." The root of the name Raghallach comes from the Gaelic word "raghallaigh," which translates to "valiant" or "courageous." Reilly is a common surname in Ireland, particularly among those with Irish ancestry, and has spread to other English-speaking countries through migration and diaspora.

Countries of origin for the last name Reilly

The last name Reilly is a surname of Irish origin, and it is predominantly found in the United States, particularly in states with a significant population of Irish Americans. The name Reilly has multiple variations, including O’Reilly, Riley, and Ryley. It derives from the Gaelic surname Ó Raghallaigh, which means “descendant of Raghallach.” The Gaelic name Raghallach is believed to come from the word “ragh,” meaning “race” or “progeny,” and the personal name “Allach,” which may refer to a mythical folk hero or warrior.

The Ó Raghallaigh clan held significant influence and power in ancient Ireland, particularly in the areas of County Cavan and County Longford. The name Reilly originated as a patronymic surname, indicating descent from a male ancestor named Raghallach. As with many Gaelic surnames, the apostrophe was later dropped in anglicized versions of the name.

Irish surnames often have multiple anglicized variations due to historical and linguistic factors, and Reilly is no exception. The variations Riley and Ryley are common adaptations of the original Reilly surname. These variations arose primarily through regional accents and dialects, as well as the individual preferences of immigrants and their descendants.

The diffusion of the Reilly surname can be attributed to the mass emigration of Irish individuals to the United States during the 19th and early 20th centuries. The Great Famine of the mid-19th century, as well as political and economic hardships, prompted millions of Irish people to seek new opportunities abroad. As a result, large Irish communities formed in various cities across America, and the Reilly surname became established within these communities.

Today, the Reilly surname is most common in states with significant Irish American populations, such as New York, Massachusetts, Illinois, and Pennsylvania. The concentration of Reillys in these regions can be attributed to the historical settlement patterns of Irish immigrants and their descendants.

While the primary origin of the Reilly surname is Irish, it is worth noting that similar surnames exist in other cultures. In some cases, individuals with the last name Reilly may have different ethnic backgrounds or ancestral origins. Therefore, it is important to consider individual family histories and genealogical research when exploring the meaning and origins of the Reilly name.

The study of surnames, known as onomastics, provides valuable insights into cultural and historical aspects of society. The Reilly surname, with its rich Gaelic origins and migration patterns, exemplifies the complexities and interconnections of human history. Exploring the Reilly name serves as a gateway to understanding the experiences and contributions of Irish Americans, as well as the broader phenomenon of surname evolution and migration patterns.

Interesting facts about the last name Reilly

  • The surname Reilly is of Irish origin and is an anglicized form of the Gaelic name Ó Raghallaigh, meaning “descendant of Raghallach.”
  • The Reilly surname is predominantly found in County Cavan and County Meath in Ireland.
  • The Ó Raghallaigh clan was historically one of the most powerful clans in medieval Ireland.
  • Reilly is one of the top 100 most common surnames in Ireland.
  • The name Reilly has various alternative spellings, including O’Reilly, O’Reille, O’Reiley, and Riley.
  • The O’Reilly family played a significant role in Irish history and produced notable figures, including Michael O’Reilly, an Irish immigrant who became a general in the Cuban army during the Spanish-American War.
  • The Reilly surname spread to other countries through Irish immigration, particularly to the United States, Canada, and Australia.
  • Actors such as John C. Reilly and Tara Reilly are examples of individuals with the surname Reilly who have achieved success in the entertainment industry.
  • Reilly is derived from the Old Irish name Raghallach, which means “valiant” or “mighty.”
  • The Reilly surname has been depicted in various literary works and novels, such as the character Detective Sergeant George Reilly in Tana French’s crime novel “The Trespasser.”

Name Rank


There are around 40884 people with the last name Reilly in the US

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