2000
#1,625
National surname rank
Recorded bearers 20,181
First available Census row
Per 100,000 7.48
Uncommon Last name
Cahill
A topographical surname of Irish origin, derived from cathail, meaning "battle", referring to someone who lived near a battlefield.
According to the 2020 US Census Bureau surname tables, roughly 23,047 Americans carry the last name Cahill. That puts it at #1,738 in the national surname ranking, appearing at a frequency of 6.72 per 100,000 people (about 1 in 14,872 residents).
This page is the full Name Census profile for the Cahill 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 Cahill with 1881 census detail, origin facts and modern UK distribution where available.
Bearers in the US
23K
1 in 14,872
Census rank
#1,738
2020 decennial data
Per 100,000
6.7
Frequency rate
Recorded bearers
20K
uncommon in the US
Popularity narrative
The Census Bureau recorded 20,098 bearers of the surname Cahill in its 2020 decennial surname file. At a rate of 6.72 per 100,000 residents, it holds the 1738th position in the national surname ranking.
Among Census respondents with the surname Cahill, the largest self-reported group is White at 91.7%. The next largest groups are Hispanic (3.4%) and Two or More Races (2.7%).
Origin
Meaning and origin of Cahill
The surname Cahill originated in Ireland, deriving from the Irish Gaelic "O'Cathail" or "O'Cathail." This name can be traced back to the 10th century and is believed to have originated in County Tipperary, where it was most prevalent. The prefix "O'" indicates a descendant of the root name, which in this case is "Cathail," an Irish personal name meaning "brave in battle."
In early Irish records, the name was often anglicized as "O'Cahill" or "O'Caughil." These variations in spelling were common due to the translation of Gaelic names into English. The earliest documented reference to the Cahill name can be found in the Annals of Inisfallen, a chronicle of medieval Irish history compiled in the late 12th century.
Throughout the centuries, the Cahill surname has been associated with several notable individuals. One prominent figure was Conor O'Cahill, a 16th-century Irish chieftain and leader of the O'Cahill clan in County Tipperary. Another was Daniel William Cahill (1775-1864), an Irish-American entrepreneur and one of the founders of the city of Brooklyn, New York.
In the literary world, the name gained recognition through James Cahill (1926-2014), an American art historian and scholar of Chinese and Japanese art. Additionally, Patrick Cahill (1925-2015) was an acclaimed American actor known for his roles in films such as "The Untouchables" and "Miller's Crossing."
The Cahill surname has also been associated with religious figures, including Reverend Thaddeus Cahill (1867-1934), an Irish-American physicist and inventor of the Telharmonium, an early electronic music synthesizer. Another notable bearer of the name was Father Patrick Cahill (1890-1959), an Irish priest and author who wrote extensively on Irish history and culture.
Over time, the Cahill surname has spread beyond Ireland and can be found in various parts of the world, particularly in countries with significant Irish diaspora populations, such as the United States, Canada, Australia, and New Zealand.
Demographics
Ancestry and ethnicity for Cahill
Among Census respondents with the surname Cahill, the largest self-reported group is White at 91.7%. The next largest groups are Hispanic (3.4%) and Two or More Races (2.7%).
The bar chart below shows how Cahill 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 Cahill surname at the time of the 2020 Census, not any inherent property of the name itself.
- White91.7% · 18,425
- Hispanic or Latino3.4% · 684
- Two or more races2.7% · 547
- Black or African American1.2% · 235
- Asian and Pacific Islander0.8% · 158
- American Indian and Alaska Native0.2% · 49
Timeline
Historical Census data for Cahill
Cahill 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
#1,737
National surname rank
Recorded bearers 20,623
+442 bearers (+2.2%)
Per 100,000 6.99
Rank movement Down 112 places
2020
#1,738
National surname rank
Recorded bearers 20,098
-525 bearers (-2.5%)
Per 100,000 6.72
Rank movement Down 1 places
| Year | Rank | Count | Per 100K | Count change | Rank change |
|---|---|---|---|---|---|
| 2000 | #1,625 | 20,181 | 7.48 | First available Census row | First available Census row |
| 2010 | #1,737 | 20,623 | 6.99 | +442 bearers (+2.2%) | Down 112 places |
| 2020 | #1,738 | 20,098 | 6.72 | -525 bearers (-2.5%) | Down 1 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 Cahill 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 | #1,737 | #1,738 | -0.1% |
| Count | 20,623 | 20,098 | -2.5% |
| Per 100K | 6.99 | 6.72 | -3.8% |
Between the 2010 and 2020 Census, the number of Cahill bearers went from 20,623 to 20,098 (-2.5% change). The surname moved down 1 positions in the national ranking, going from #1,737 to #1,738.
FAQ
Cahill surname: questions and answers
How many people in the U.S. have the surname Cahill?
Name Census estimates that about 23,047 living Americans carry the surname Cahill. Using the current population baseline, that works out to roughly 1 in 14,872 residents.
How common is Cahill?
Cahill ranks #1,738 in the 2020 Census surname tables and is classified on this site as "Uncommon." The Census recorded the name at a frequency of 6.72 per 100,000 residents, which is about 7 people out of every 100,000.
How many people with this surname were counted in the Census?
The raw 2020 Census file counted 20,098 people with the surname Cahill. That is different from the site's living-bearer estimate (23,047), which projects the surname's present-day count by applying the Census frequency rate to the current U.S. population.
What does 6.72 per 100,000 actually mean?
It is the Census Bureau's normalized frequency measure. A rate of 6.72 per 100,000 means that if you picked a random group of 100,000 U.S. residents, you would expect about 7 of them to have the surname Cahill.
Has Cahill become more or less common over time?
Between 2010 and 2020, the surname Cahill went from 20,623 recorded bearers to 20,098. That is a decrease of 525 (-2.5%). In the national ranking it fell from #1,737 to #1,738.
What does the Census say about the background of Cahill?
Among Census respondents with the surname Cahill, the largest self-reported group is White at 91.7%. The next largest groups are Hispanic (3.4%) and Two or More Races (2.7%). 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 Cahill in the 2020 Census, accounting for 91.7% (18,425 people in the source table).
What is the full ancestry breakdown?
Cahill appears across multiple self-reported groups in the Census data. The largest shares in the 2020 file are White (91.7%), Hispanic (3.4%), Two or More Races (2.7%). 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 Cahill (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 Cahill mean?
A topographical surname of Irish origin, derived from cathail, meaning "battle", referring to someone who lived near a battlefield. 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 Cahill (6.72 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 have the last name Cahill?
See how many people are called Cahill on HowManyOfMe.org, our sister site built around that single question.