Find out how popular the last name O'Reilly is in the United States and learn more about the meaning, history, and race and ethnic origin of people in America who are named O'Reilly.

O'Reilly, like all of the last names we have data for, is identified by the U.S. Census Bureau as a surname which has more than 100 occurrences in the United States in the Decennial Census survey. The most recent statistics we have for the O'Reilly surname is from the 2010 census data.

Popularity of O'Reilly in America

O'Reilly is the 2970th most popular name in America based on the data we have collected from the U.S. Census Bureau.

The O'Reilly surname appeared 12,074 times in the 2010 census and if you were to sample 100,000 people in the United States, approximately 4 people would have the surname O'Reilly.

We can also compare 2010 data for O'Reilly to data from the previous census in 2000. The table below contains all of the statistics for both years in a side-by-side comparison.

The history of the last name O'Reilly

The surname O'Reilly is of Irish origin and dates back to the 11th century. It is derived from the Gaelic name Ó Raghallaigh, which means "descendant of Raghallach". The name Raghallach is a combination of the words "ragh", meaning "fortune", and "allach", meaning "prosperous" or "wealthy".

The O'Reillys were one of the most prominent and influential families in the ancient kingdom of East Bréifne, which covered parts of modern-day counties Cavan and Leitrim. They were lords of East Bréifne from the 11th century until the 17th century, and their stronghold was at Cavan town.

One of the earliest recorded mentions of the name can be found in the Annals of the Four Masters, a chronicle of medieval Irish history compiled in the 17th century. The annals document the exploits of various O'Reilly chieftains and their role in the political and military affairs of the region.

The name O'Reilly first appears in English records in the 13th century, with various spellings such as O'Reily, O'Reiley, and O'Rely. The Domesday Book, a historical record commissioned by William the Conqueror in 1086, does not include any references to the name, as it was a survey of landholders in England and parts of Wales.

Notable figures with the surname O'Reilly throughout history include:

1. Sir John O'Reilly (c. 1497 - 1562), an Irish chieftain and Lord of East Bréifne who played a significant role in the political and military struggles of 16th century Ireland.

2. Andrew O'Reilly (1742 - 1832), an Irish-born Spanish general who served in the Spanish Army during the American Revolutionary War and the Peninsular War against Napoleonic France.

3. Jeremiah O'Reilly (1831 - 1896), an Irish-American Catholic priest and president of the University of Notre Dame from 1864 to 1866.

4. John Boyle O'Reilly (1844 - 1890), an Irish-born American poet, novelist, and journalist who was a leading voice for Irish independence in the United States.

5. Mary O'Reilly (1888 - 1963), an Irish revolutionary and member of the Irish Republican Army who played a significant role in the Irish War of Independence and the Irish Civil War.

Race and ethnic origin of people with the last name O'Reilly

We also have some data on the ancestry of people with the surname O'Reilly.

The below race categories are the modified race categories used in the Census Bureau's population estimates program. All people were categorized into six mutually exclusive racial and Hispanic origin groups:

1. White only
2. Black only
3. American Indian and Alaskan Native only
4. Asian and Pacific Islander only
5. Hispanic
6. Two or More Races

For the most recent 2010 census data, the race/ethnic origin breakdown for O'Reilly was:

Note: Any fields showing (S) means the data was suppressed for privacy so that the data does not in any way identify any specific individuals.

Since we have data from the previous census in 2000, we can also compare the values to see how the popularity of O'Reilly has changed in the 10 years between the two census surveys.

Data source

The last name data and ethnic breakdown of last names is sourced directly from the Decennial Census survey, conducted every 10 years by the United States Census Bureau.

The history and meaning of the name O'Reilly was researched and written by our team of onomatology and genealogy experts.

If you have a correction or suggestion to improve the history of O'Reilly, please contact us.

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