2000
#10,588
National surname rank
Recorded bearers 2,779
First available Census row
Per 100,000 1.03
Rare Last name
Ocallaghan
A surname of Irish origin, derived from the Gaelic "Ó Ceallacháin," meaning "descendant of Ceallachán" (a personal name meaning "bright-headed").
According to the 2020 US Census Bureau surname tables, roughly 3,527 Americans carry the last name Ocallaghan. That puts it at #10,003 in the national surname ranking, appearing at a frequency of 1.03 per 100,000 people (about 1 in 97,180 residents).
This page is the full Name Census profile for the Ocallaghan 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 Ocallaghan with 1881 census detail, origin facts and modern UK distribution where available.
Bearers in the US
3.5K
1 in 97,180
Census rank
#10,003
2020 decennial data
Per 100,000
1.0
Frequency rate
Recorded bearers
3.1K
rare in the US
Popularity narrative
The Census Bureau recorded 3,076 bearers of the surname Ocallaghan in its 2020 decennial surname file. At a rate of 1.03 per 100,000 residents, it holds the 10003rd position in the national surname ranking.
Among Census respondents with the surname Ocallaghan, the largest self-reported group is White at 92.8%. The next largest groups are Hispanic (3.3%) and Two or More Races (2.3%).
Origin
Meaning and origin of Ocallaghan
The surname O'Callaghan is of Irish origin, deriving from the Gaelic Ó Ceallacháin, meaning "descendant of Ceallachán". Ceallachán was an ancient Irish personal name, which potentially contained elements referring to "bright-headed" or "frequenting churches".
The name originated in County Cork, where the O'Callaghans were a notable family of the Uí Duinnchuan sept. The first recorded instance of the name dates back to the 13th century, with references to Dermot O'Callaghan, a prominent member of the clan during that period.
In the 16th century, the O'Callaghans were involved in the Second Desmond Rebellion against English rule in Ireland. Cormac O'Callaghan, born around 1550, was a notable figure in this conflict, leading the clan's forces alongside the Earl of Desmond.
The O'Callaghan name appears in various historical records, including the Annals of Inisfallen and the Annals of the Four Masters, which chronicle events in medieval Ireland. These sources mention several noteworthy individuals bearing the surname.
One of the earliest documented instances of the name is found in the Domesday Book of 1086, where a person named Gillebertus Challan is listed as a landowner in Lincolnshire, England. This entry may represent an early variant spelling of the name.
Throughout history, several prominent individuals have carried the O'Callaghan surname. These include:
1. Jeremiah O'Callaghan (1805-1880), an Irish-American politician who served as a member of the United States House of Representatives from New York.
2. Sir Ralph O'Callaghan (1854-1937), an Irish businessman and politician who served as Lord Mayor of Dublin in the early 20th century.
3. Sean O'Callaghan (born 1954), an Irish author and former member of the Provisional Irish Republican Army (IRA) who later became an informant for the British government.
4. Conor O'Callaghan (born 1968), an Irish poet and novelist who has received numerous literary awards for his works.
5. Rory O'Callaghan (1961-2022), an Irish actor known for his roles in films such as "The Boxer" and "The Snapper".
The O'Callaghan name has also been associated with various place names in Ireland, such as Callaghanstown and Callaghan's Bridge, further emphasizing its deep roots in the region.
Demographics
Ancestry and ethnicity for Ocallaghan
Among Census respondents with the surname Ocallaghan, the largest self-reported group is White at 92.8%. The next largest groups are Hispanic (3.3%) and Two or More Races (2.3%).
The bar chart below shows how Ocallaghan 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 Ocallaghan surname at the time of the 2020 Census, not any inherent property of the name itself.
- White92.8% · 2,854
- Hispanic or Latino3.3% · 101
- Two or more races2.3% · 71
- Asian and Pacific Islander1.3% · 40
- Black or African American0.3% · 9
- American Indian and Alaska Native0.0% · 1
Timeline
Historical Census data for Ocallaghan
Ocallaghan 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
#10,626
National surname rank
Recorded bearers 3,014
+235 bearers (+8.5%)
Per 100,000 1.02
Rank movement Down 38 places
2020
#10,003
National surname rank
Recorded bearers 3,076
+62 bearers (+2.1%)
Per 100,000 1.03
Rank movement Up 623 places
| Year | Rank | Count | Per 100K | Count change | Rank change |
|---|---|---|---|---|---|
| 2000 | #10,588 | 2,779 | 1.03 | First available Census row | First available Census row |
| 2010 | #10,626 | 3,014 | 1.02 | +235 bearers (+8.5%) | Down 38 places |
| 2020 | #10,003 | 3,076 | 1.03 | +62 bearers (+2.1%) | Up 623 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 Ocallaghan 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 | #10,626 | #10,003 | 5.9% |
| Count | 3,014 | 3,076 | 2.1% |
| Per 100K | 1.02 | 1.03 | 0.9% |
Between the 2010 and 2020 Census, the number of Ocallaghan bearers went from 3,014 to 3,076 (+2.1% change). The surname moved up 623 positions in the national ranking, going from #10,626 to #10,003.
Notable bearers
Famous people with the surname Ocallaghan
FAQ
Ocallaghan surname: questions and answers
How many people in the U.S. have the surname Ocallaghan?
Name Census estimates that about 3,527 living Americans carry the surname Ocallaghan. Using the current population baseline, that works out to roughly 1 in 97,180 residents.
How common is Ocallaghan?
Ocallaghan ranks #10,003 in the 2020 Census surname tables and is classified on this site as "Rare." The Census recorded the name at a frequency of 1.03 per 100,000 residents, which is about 1 people out of every 100,000.
How many people with this surname were counted in the Census?
The raw 2020 Census file counted 3,076 people with the surname Ocallaghan. That is different from the site's living-bearer estimate (3,527), which projects the surname's present-day count by applying the Census frequency rate to the current U.S. population.
What does 1.03 per 100,000 actually mean?
It is the Census Bureau's normalized frequency measure. A rate of 1.03 per 100,000 means that if you picked a random group of 100,000 U.S. residents, you would expect about 1 of them to have the surname Ocallaghan.
Has Ocallaghan become more or less common over time?
Between 2010 and 2020, the surname Ocallaghan went from 3,014 recorded bearers to 3,076. That is an increase of 62 (+2.1%). In the national ranking it rose from #10,626 to #10,003.
What does the Census say about the background of Ocallaghan?
Among Census respondents with the surname Ocallaghan, the largest self-reported group is White at 92.8%. The next largest groups are Hispanic (3.3%) and Two or More Races (2.3%). 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 Ocallaghan in the 2020 Census, accounting for 92.8% (2,854 people in the source table).
What is the full ancestry breakdown?
Ocallaghan appears across multiple self-reported groups in the Census data. The largest shares in the 2020 file are White (92.8%), Hispanic (3.3%), Two or More Races (2.3%). 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 Ocallaghan (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 Ocallaghan mean?
A surname of Irish origin, derived from the Gaelic "Ó Ceallacháin," meaning "descendant of Ceallachán" (a personal name meaning "bright-headed"). 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 Ocallaghan (1.03 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 Americans have the surname Ocallaghan?
For a quick modern estimate, our sister site HowManyOfMe.org answers that in one glance, with the living-bearer count front and centre.