2000
#144,908
National surname rank
Recorded bearers 105
First available Census row
Per 100,000 0.04
Very Rare Last name
Gillahan
An Anglicized form of the Irish surname Ó Gillacháin, meaning "descendant of the servant of Saint John".
According to the 2020 US Census Bureau surname tables, roughly 114 Americans carry the last name Gillahan. That puts it at #156,005 in the national surname ranking, appearing at a frequency of 0.03 per 100,000 people (about 1 in 3,006,617 residents).
This page is the full Name Census profile for the Gillahan 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.
Bearers in the US
114
1 in 3,006,617
Census rank
#156,005
2020 decennial data
Per 100,000
0.0
Frequency rate
Recorded bearers
99
very rare in the US
Popularity narrative
The Census Bureau recorded 99 bearers of the surname Gillahan in its 2020 decennial surname file. At a rate of 0.03 per 100,000 residents, it holds the 156005th position in the national surname ranking.
Among Census respondents with the surname Gillahan, the largest self-reported group is White at 94.9%. The next largest groups are Hispanic (5.1%).
Origin
Meaning and origin of Gillahan
The surname Gillahan is of Irish origin, deriving from the Gaelic name Ó Gillacháin, meaning "descendant of Gillachán." The name Gillachán is a diminutive form of the personal name Gilla, meaning "servant" or "devotee," combined with a diminutive suffix.
The earliest recorded instances of the name Gillahan can be traced back to County Donegal in Ulster, Ireland, during the 16th century. The name was particularly prevalent in the parish of Inishkeel, located in the Glenties area of southwest Donegal.
In the Annals of the Four Masters, a chronicle of medieval Irish history, there are several references to individuals bearing the surname Gillahan or its various spellings, such as O'Gillagain and O'Gilligan. One notable entry mentions a Gillachán Ó Gillacháin, who was a member of the clergy in the 15th century.
During the 17th century, the name Gillahan began to spread beyond Donegal as a result of the Plantation of Ulster, a government-sponsored initiative to settle English and Scottish Protestant settlers in Ireland. Some Gillahans were among the Irish Catholic families displaced by this colonization effort, leading to the dispersal of the name throughout other parts of Ireland and beyond.
One of the earliest recorded instances of the name outside of Ireland is found in the Hearth Money Rolls of County Durham, England, in 1666, which lists a James Gillahan as a resident.
Notable individuals with the surname Gillahan include:
1. Patrick Gillahan (1777-1850), an Irish-American politician who served as a member of the Pennsylvania House of Representatives.
2. Michael Gillahan (1844-1917), an Irish-born American Catholic priest and educator who founded several schools in Pennsylvania.
3. James Gillahan (1860-1940), an Irish-American businessman and real estate developer in Pittsburgh, Pennsylvania.
4. Thomas Gillahan (1875-1951), an Irish-American professional baseball player who played for the Philadelphia Phillies in the early 20th century.
5. John Gillahan (1892-1967), an Irish-American politician who served as the Mayor of Pittsburgh, Pennsylvania, from 1959 to 1964.
While the surname Gillahan has dispersed globally over the centuries, its roots can be traced back to the ancient Irish kingdom of Tír Chonaill (County Donegal), where it originated as a personal name reflecting devotion and service to a religious or noble patron.
Demographics
Ancestry and ethnicity for Gillahan
Among Census respondents with the surname Gillahan, the largest self-reported group is White at 94.9%. The next largest groups are Hispanic (5.1%).
The bar chart below shows how Gillahan 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 Gillahan surname at the time of the 2020 Census, not any inherent property of the name itself.
- White94.9% · 94
- Hispanic or Latino5.1% · 5
Timeline
Historical Census data for Gillahan
Gillahan 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
#146,201
National surname rank
Recorded bearers 113
+8 bearers (+7.6%)
Per 100,000 0.04
Rank movement Down 1,293 places
2020
#156,005
National surname rank
Recorded bearers 99
-14 bearers (-12.4%)
Per 100,000 0.03
Rank movement Down 9,804 places
| Year | Rank | Count | Per 100K | Count change | Rank change |
|---|---|---|---|---|---|
| 2000 | #144,908 | 105 | 0.04 | First available Census row | First available Census row |
| 2010 | #146,201 | 113 | 0.04 | +8 bearers (+7.6%) | Down 1,293 places |
| 2020 | #156,005 | 99 | 0.03 | -14 bearers (-12.4%) | Down 9,804 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 Gillahan 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 | #146,201 | #156,005 | -6.7% |
| Count | 113 | 99 | -12.4% |
| Per 100K | 0.04 | 0.03 | -17.2% |
Between the 2010 and 2020 Census, the number of Gillahan bearers went from 113 to 99 (-12.4% change). The surname moved down 9,804 positions in the national ranking, going from #146,201 to #156,005.
FAQ
Gillahan surname: questions and answers
How many people in the U.S. have the surname Gillahan?
Name Census estimates that about 114 living Americans carry the surname Gillahan. Using the current population baseline, that works out to roughly 1 in 3,006,617 residents.
How common is Gillahan?
Gillahan ranks #156,005 in the 2020 Census surname tables and is classified on this site as "Very Rare." The Census recorded the name at a frequency of 0.03 per 100,000 residents, which is about 0 people out of every 100,000.
How many people with this surname were counted in the Census?
The raw 2020 Census file counted 99 people with the surname Gillahan. That is different from the site's living-bearer estimate (114), which projects the surname's present-day count by applying the Census frequency rate to the current U.S. population.
What does 0.03 per 100,000 actually mean?
It is the Census Bureau's normalized frequency measure. A rate of 0.03 per 100,000 means that if you picked a random group of 100,000 U.S. residents, you would expect about 0 of them to have the surname Gillahan.
Has Gillahan become more or less common over time?
Between 2010 and 2020, the surname Gillahan went from 113 recorded bearers to 99. That is a decrease of 14 (-12.4%). In the national ranking it fell from #146,201 to #156,005.
What does the Census say about the background of Gillahan?
Among Census respondents with the surname Gillahan, the largest self-reported group is White at 94.9%. The next largest groups are Hispanic (5.1%). 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 Gillahan in the 2020 Census, accounting for 94.9% (94 people in the source table).
What is the full ancestry breakdown?
Gillahan appears across multiple self-reported groups in the Census data. The largest shares in the 2020 file are White (94.9%), Hispanic (5.1%). 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 Gillahan (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 Gillahan mean?
An Anglicized form of the Irish surname Ó Gillacháin, meaning "descendant of the servant of Saint John". 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 Gillahan (0.03 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 Gillahan?
For a faster, more casual read, check HowManyOfMe.org — our sister site built around that single question.