2000
#15,780
National surname rank
Recorded bearers 1,696
First available Census row
Per 100,000 0.63
Rare Last name
Dennehy
Anglicized form of the Irish surname Ó Denaí meaning descendant of Dena.
According to the 2020 US Census Bureau surname tables, roughly 1,929 Americans carry the last name Dennehy. That puts it at #16,566 in the national surname ranking, appearing at a frequency of 0.56 per 100,000 people (about 1 in 177,685 residents).
This page is the full Name Census profile for the Dennehy 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 Dennehy with 1881 census detail, origin facts and modern UK distribution where available.
Bearers in the US
1.9K
1 in 177,685
Census rank
#16,566
2020 decennial data
Per 100,000
0.6
Frequency rate
Recorded bearers
1.7K
rare in the US
Popularity narrative
The Census Bureau recorded 1,682 bearers of the surname Dennehy in its 2020 decennial surname file. At a rate of 0.56 per 100,000 residents, it holds the 16566th position in the national surname ranking.
Among Census respondents with the surname Dennehy, the largest self-reported group is White at 90.5%. The next largest groups are Hispanic (4.6%) and Two or More Races (2.2%).
Origin
Meaning and origin of Dennehy
The surname Dennehy originated in Ireland and is derived from the Gaelic Ó Dónaigh, meaning "descendant of Donnchadh." Donnchadh was a personal name that meant "brown warrior" or "dark chief." The name Dennehy is an anglicized version of the original Gaelic form.
The surname Dennehy has its roots in County Cork, Ireland, where it was concentrated in the baronies of Duhallow and Muskerry. It is believed that the Dennehy clan descended from the Uí Duinnchuan, a branch of the Uí Fidgenti, who were a powerful family in the area.
One of the earliest recorded instances of the name Dennehy can be found in the Annals of Inisfallen, a chronicle compiled in the early 12th century. The annals mention a Donnchadh Ua Dónaigh, who was the chief of Hy-Duinnchuain, in the year 1027.
In the 16th century, the Dennehy family was prominent in the area of Muskerry, County Cork. During this period, several members of the family held positions of influence, including Tadhg Dennehy, who was the Bishop of Ross from 1536 to 1554.
Another notable figure was Donnchadh Dennehy, who lived in the late 16th century and was a renowned Irish poet and scholar. His work, known as the "Dánta Donnchadha Uí Dhónaigh," is a valuable source of information about the history and culture of the Gaelic Irish.
In the 17th century, the Dennehy family faced challenges due to the Cromwellian conquest of Ireland and the subsequent confiscation of lands. Despite this, the family maintained a presence in County Cork, and some members emigrated to other parts of Ireland and abroad.
One prominent individual from this period was John Dennehy, who was born in County Cork in 1678. He was a Catholic priest and a prominent figure in the Irish Jacobite movement, which sought to restore the Catholic Stuart monarch to the thrones of England, Scotland, and Ireland.
Fast-forwarding to the 19th century, we find James Dennehy, who was born in 1826 in County Cork. He was a renowned Irish artist and painter, known for his landscapes and portraits depicting the life and scenery of his native county.
In the 20th century, the name Dennehy continued to be associated with various fields, including politics, literature, and the arts. One notable figure was Brian Dennehy, an American actor born in 1938 in Bridgeport, Connecticut, to Irish immigrant parents. He had a successful career in films, television, and theater, earning numerous awards and nominations for his performances.
Demographics
Ancestry and ethnicity for Dennehy
Among Census respondents with the surname Dennehy, the largest self-reported group is White at 90.5%. The next largest groups are Hispanic (4.6%) and Two or More Races (2.2%).
The bar chart below shows how Dennehy 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 Dennehy surname at the time of the 2020 Census, not any inherent property of the name itself.
- White90.5% · 1,523
- Hispanic or Latino4.6% · 77
- Two or more races2.2% · 37
- Asian and Pacific Islander1.2% · 21
- Black or African American0.9% · 15
- American Indian and Alaska Native0.5% · 9
Timeline
Historical Census data for Dennehy
Dennehy 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
#16,544
National surname rank
Recorded bearers 1,735
+39 bearers (+2.3%)
Per 100,000 0.59
Rank movement Down 764 places
2020
#16,566
National surname rank
Recorded bearers 1,682
-53 bearers (-3.1%)
Per 100,000 0.56
Rank movement Down 22 places
| Year | Rank | Count | Per 100K | Count change | Rank change |
|---|---|---|---|---|---|
| 2000 | #15,780 | 1,696 | 0.63 | First available Census row | First available Census row |
| 2010 | #16,544 | 1,735 | 0.59 | +39 bearers (+2.3%) | Down 764 places |
| 2020 | #16,566 | 1,682 | 0.56 | -53 bearers (-3.1%) | Down 22 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 Dennehy 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 | #16,544 | #16,566 | -0.1% |
| Count | 1,735 | 1,682 | -3.1% |
| Per 100K | 0.59 | 0.56 | -4.6% |
Between the 2010 and 2020 Census, the number of Dennehy bearers went from 1,735 to 1,682 (-3.1% change). The surname moved down 22 positions in the national ranking, going from #16,544 to #16,566.
Notable bearers
Famous people with the surname Dennehy
FAQ
Dennehy surname: questions and answers
How many people in the U.S. have the surname Dennehy?
Name Census estimates that about 1,929 living Americans carry the surname Dennehy. Using the current population baseline, that works out to roughly 1 in 177,685 residents.
How common is Dennehy?
Dennehy ranks #16,566 in the 2020 Census surname tables and is classified on this site as "Rare." The Census recorded the name at a frequency of 0.56 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 1,682 people with the surname Dennehy. That is different from the site's living-bearer estimate (1,929), which projects the surname's present-day count by applying the Census frequency rate to the current U.S. population.
What does 0.56 per 100,000 actually mean?
It is the Census Bureau's normalized frequency measure. A rate of 0.56 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 Dennehy.
Has Dennehy become more or less common over time?
Between 2010 and 2020, the surname Dennehy went from 1,735 recorded bearers to 1,682. That is a decrease of 53 (-3.1%). In the national ranking it fell from #16,544 to #16,566.
What does the Census say about the background of Dennehy?
Among Census respondents with the surname Dennehy, the largest self-reported group is White at 90.5%. The next largest groups are Hispanic (4.6%) and Two or More Races (2.2%). 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 Dennehy in the 2020 Census, accounting for 90.5% (1,523 people in the source table).
What is the full ancestry breakdown?
Dennehy appears across multiple self-reported groups in the Census data. The largest shares in the 2020 file are White (90.5%), Hispanic (4.6%), Two or More Races (2.2%). 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 Dennehy (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 Dennehy mean?
Anglicized form of the Irish surname Ó Denaí meaning descendant of Dena. 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 Dennehy (0.56 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 are called Dennehy?
See how many people have the last name Dennehy on HowManyOfMe.org, our sister site built around that single question.