2000
#2,946
National surname rank
Recorded bearers 11,224
First available Census row
Per 100,000 4.16
Uncommon Last name
Oreilly
A surname of Irish origin, derived from the Gaelic "Ó Raghallaigh," meaning "descendant of Raghallach" (a personal name meaning "valiant").
According to the 2020 US Census Bureau surname tables, roughly 13,833 Americans carry the last name Oreilly. That puts it at #2,913 in the national surname ranking, appearing at a frequency of 4.04 per 100,000 people (about 1 in 24,778 residents).
This page is the full Name Census profile for the Oreilly surname. You will find the Census Bureau frequency data, a multi-census history view, an ancestry and ethnicity breakdown based on self-reported demographics, the name's meaning and origin where available, and answers to the most common questions people ask about this surname.
For British records, Name Census UK has a British surname profile for Oreilly with 1881 census detail, origin facts and modern UK distribution where available.
Bearers in the US
14K
1 in 24,778
Census rank
#2,913
2020 decennial data
Per 100,000
4.0
Frequency rate
Recorded bearers
12K
uncommon in the US
Popularity narrative
The Census Bureau recorded 12,063 bearers of the surname Oreilly in its 2020 decennial surname file. At a rate of 4.04 per 100,000 residents, it holds the 2913th position in the national surname ranking.
Among Census respondents with the surname Oreilly, the largest self-reported group is White at 89.0%. The next largest groups are Hispanic (4.7%) and Two or More Races (3.2%).
Origin
Meaning and origin of Oreilly
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.
Demographics
Ancestry and ethnicity for Oreilly
Among Census respondents with the surname Oreilly, the largest self-reported group is White at 89.0%. The next largest groups are Hispanic (4.7%) and Two or More Races (3.2%).
The bar chart below shows how Oreilly bearers described their own race and ethnicity on the 2020 Census form. The Census Bureau groups responses into six broad categories: White, Black or African American, Hispanic or Latino, Asian and Pacific Islander, American Indian and Alaska Native, and Two or More Races. When a category has too few respondents for a given surname, the Bureau suppresses the figure to protect individual privacy, which is why some names show fewer than six slices.
Percentages are shown for every Census year so the breakdown stays comparable over time. When the source file also includes raw headcounts, Name Census shows those alongside the percentages in the legend.
Keep in mind that these are self-reported numbers. A person's surname does not determine their race or ethnicity, and the distribution you see here reflects the specific population who happened to carry the Oreilly surname at the time of the 2020 Census, not any inherent property of the name itself.
- White89.0% · 10,731
- Hispanic or Latino4.7% · 566
- Two or more races3.2% · 390
- Black or African American2.0% · 239
- Asian and Pacific Islander0.8% · 102
- American Indian and Alaska Native0.3% · 35
Timeline
Historical Census data for Oreilly
Oreilly appears in 3 published Census surname files: 2000, 2010, 2020. The cards below show how the name's rank and bearer count changed across each release.
2010
#2,970
National surname rank
Recorded bearers 12,074
+850 bearers (+7.6%)
Per 100,000 4.09
Rank movement Down 24 places
2020
#2,913
National surname rank
Recorded bearers 12,063
-11 bearers (-0.1%)
Per 100,000 4.04
Rank movement Up 57 places
| Year | Rank | Count | Per 100K | Count change | Rank change |
|---|---|---|---|---|---|
| 2000 | #2,946 | 11,224 | 4.16 | First available Census row | First available Census row |
| 2010 | #2,970 | 12,074 | 4.09 | +850 bearers (+7.6%) | Down 24 places |
| 2020 | #2,913 | 12,063 | 4.04 | -11 bearers (-0.1%) | Up 57 places |
For 2020, the Census Bureau published race and Hispanic-origin columns as counts rather than percentages. Name Census converts those counts back into shares so the ancestry section stays comparable with the older surname files.
Year on year
2010 vs 2020 Census
How has the Oreilly surname changed between Census years? The chart shows bearer count side by side, and the table compares rank, count, and frequency.
Census year comparison
20102020
| Metric | 2010 | 2020 | Change |
|---|---|---|---|
| Rank | #2,970 | #2,913 | 1.9% |
| Count | 12,074 | 12,063 | -0.1% |
| Per 100K | 4.09 | 4.04 | -1.3% |
Between the 2010 and 2020 Census, the number of Oreilly bearers went from 12,074 to 12,063 (-0.1% change). The surname moved up 57 positions in the national ranking, going from #2,970 to #2,913.
Notable bearers
Famous people with the surname Oreilly
FAQ
Oreilly surname: questions and answers
How many people in the U.S. have the surname Oreilly?
Name Census estimates that about 13,833 living Americans carry the surname Oreilly. Using the current population baseline, that works out to roughly 1 in 24,778 residents.
How common is Oreilly?
Oreilly ranks #2,913 in the 2020 Census surname tables and is classified on this site as "Uncommon." The Census recorded the name at a frequency of 4.04 per 100,000 residents, which is about 4 people out of every 100,000.
How many people with this surname were counted in the Census?
The raw 2020 Census file counted 12,063 people with the surname Oreilly. That is different from the site's living-bearer estimate (13,833), which projects the surname's present-day count by applying the Census frequency rate to the current U.S. population.
What does 4.04 per 100,000 actually mean?
It is the Census Bureau's normalized frequency measure. A rate of 4.04 per 100,000 means that if you picked a random group of 100,000 U.S. residents, you would expect about 4 of them to have the surname Oreilly.
Has Oreilly become more or less common over time?
Between 2010 and 2020, the surname Oreilly went from 12,074 recorded bearers to 12,063. That is a decrease of 11 (-0.1%). In the national ranking it rose from #2,970 to #2,913.
What does the Census say about the background of Oreilly?
Among Census respondents with the surname Oreilly, the largest self-reported group is White at 89.0%. The next largest groups are Hispanic (4.7%) and Two or More Races (3.2%). These figures come from the 2020 Census Bureau surname tables, based on how respondents described their own race and ethnicity.
Which group reports this surname most often?
White is the largest self-reported group for the surname Oreilly in the 2020 Census, accounting for 89.0% (10,731 people in the source table).
What is the full ancestry breakdown?
Oreilly appears across multiple self-reported groups in the Census data. The largest shares in the 2020 file are White (89.0%), Hispanic (4.7%), Two or More Races (3.2%). For 2020, the source file also published raw headcounts for each group, which is why this page can show both percentages and counts in the ancestry section.
Is this page using the latest Census data?
Yes. This page is using the latest surname file currently loaded on Name Census, which is 2020. The historical section above also keeps any older Census surname entries we have for Oreilly (2000, 2010, 2020).
Does the Census include every surname?
No. The Census Bureau only publishes surnames that appeared at least 100 times in a given decennial Census. That means very rare surnames are excluded entirely, and a surname can appear in one Census release but disappear from a later one if it falls below the reporting threshold.
Why don't the ancestry percentages always add up to exactly 100%?
There are two main reasons: rounding and suppression. The Census Bureau rounds published values, and it may suppress very small cells to protect privacy. For 2020, the Bureau also published raw group counts rather than direct percentages, so Name Census converts those counts back into shares for comparability across census years.
What does Oreilly mean?
A surname of Irish origin, derived from the Gaelic "Ó Raghallaigh," meaning "descendant of Raghallach" (a personal name meaning "valiant"). The fuller origin note on this page goes into more detail.
Where does the surname data come from?
All surname statistics on Name Census are drawn from the US Census Bureau's decennial surname frequency tables. These files list every surname that appeared 100 or more times in the 2020 Census, along with a count, a per-100,000 rate, and a self-reported demographic breakdown. You can read the full explanation on our methodology page.
How does Name Census estimate living bearers?
For surnames, Name Census does not age cohorts the way it does for first names. Instead, it takes the Census Bureau's published frequency for Oreilly (4.04 per 100,000) and applies that rate to the current U.S. resident population to estimate how many living Americans have the surname today.
How many people share the surname Oreilly?
For a quick modern estimate, our sister site HowManyOfMe.org answers that in one glance, with the living-bearer count front and centre.