2000
#138,741
National surname rank
Recorded bearers 111
First available Census row
Per 100,000 0.04
Very Rare Last name
Kilfoy
An Anglicized form of the Irish Gaelic surname Ó Cilfeadha meaning descendant of the devotee.
According to the 2020 US Census Bureau surname tables, roughly 118 Americans carry the last name Kilfoy. That puts it at #154,182 in the national surname ranking, appearing at a frequency of 0.03 per 100,000 people (about 1 in 2,904,698 residents).
This page is the full Name Census profile for the Kilfoy 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
118
1 in 2,904,698
Census rank
#154,182
2020 decennial data
Per 100,000
0.0
Frequency rate
Recorded bearers
103
very rare in the US
Popularity narrative
The Census Bureau recorded 103 bearers of the surname Kilfoy in its 2020 decennial surname file. At a rate of 0.03 per 100,000 residents, it holds the 154182nd position in the national surname ranking.
Among Census respondents with the surname Kilfoy, the largest self-reported group is White at 89.3%. The next largest groups are Hispanic (5.8%) and American Indian/Alaska Native (1.9%).
Origin
Meaning and origin of Kilfoy
The surname KILFOY has its origins in Ireland, tracing back to the 16th century. It is derived from the Irish Gaelic words "cill" meaning church and "fhuadach" meaning banishment or exile. The name likely referred to someone who was exiled from a church or monastic settlement.
One of the earliest recorded instances of the name is found in the Annals of the Four Masters, a chronicle of medieval Irish history, which mentions a Diarmaid Killfoy in the year 1591. This suggests the surname was already established by the late 16th century.
In the 17th century, the name appears in various parish records and land registers across counties like Donegal, Sligo, and Mayo in the northwestern part of Ireland. The spelling variations include Kilfoy, Killfoy, Killfae, and Kilfae, reflecting the phonetic adaptations common in the translation from Irish to English.
A notable bearer of the name was Patrick Kilfoy, a Catholic priest born in County Sligo around 1650. He was involved in the Jacobite uprisings in support of the deposed King James II and was imprisoned for a time in the late 17th century.
In the early 19th century, a John Kilfoy from County Mayo was known for his involvement in the Irish Rebellion of 1798, fighting against British rule. He was later pardoned and lived until 1835.
Another figure of historical significance was Bridget Kilfoy, born in County Donegal in 1829. She was a prominent advocate for women's rights and education in Ireland during the late 19th century.
The name also has a connection to place names in Ireland. The townland of Kilfoy in County Donegal likely derived its name from the surname, indicating a settlement associated with the family.
While the name KILFOY is relatively uncommon, it has persisted through the centuries, with bearers scattered across Ireland and, in more recent times, in Irish diaspora communities around the world.
Demographics
Ancestry and ethnicity for Kilfoy
Among Census respondents with the surname Kilfoy, the largest self-reported group is White at 89.3%. The next largest groups are Hispanic (5.8%) and American Indian/Alaska Native (1.9%).
The bar chart below shows how Kilfoy 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 Kilfoy surname at the time of the 2020 Census, not any inherent property of the name itself.
- White89.3% · 92
- Hispanic or Latino5.8% · 6
- American Indian and Alaska Native1.9% · 2
- Two or more races1.9% · 2
- Asian and Pacific Islander1.0% · 1
Timeline
Historical Census data for Kilfoy
Kilfoy 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
#150,452
National surname rank
Recorded bearers 109
-2 bearers (-1.8%)
Per 100,000 0.04
Rank movement Down 11,711 places
2020
#154,182
National surname rank
Recorded bearers 103
-6 bearers (-5.5%)
Per 100,000 0.03
Rank movement Down 3,730 places
| Year | Rank | Count | Per 100K | Count change | Rank change |
|---|---|---|---|---|---|
| 2000 | #138,741 | 111 | 0.04 | First available Census row | First available Census row |
| 2010 | #150,452 | 109 | 0.04 | -2 bearers (-1.8%) | Down 11,711 places |
| 2020 | #154,182 | 103 | 0.03 | -6 bearers (-5.5%) | Down 3,730 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 Kilfoy 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 | #150,452 | #154,182 | -2.5% |
| Count | 109 | 103 | -5.5% |
| Per 100K | 0.04 | 0.03 | -13.9% |
Between the 2010 and 2020 Census, the number of Kilfoy bearers went from 109 to 103 (-5.5% change). The surname moved down 3,730 positions in the national ranking, going from #150,452 to #154,182.
FAQ
Kilfoy surname: questions and answers
How many people in the U.S. have the surname Kilfoy?
Name Census estimates that about 118 living Americans carry the surname Kilfoy. Using the current population baseline, that works out to roughly 1 in 2,904,698 residents.
How common is Kilfoy?
Kilfoy ranks #154,182 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 103 people with the surname Kilfoy. That is different from the site's living-bearer estimate (118), 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 Kilfoy.
Has Kilfoy become more or less common over time?
Between 2010 and 2020, the surname Kilfoy went from 109 recorded bearers to 103. That is a decrease of 6 (-5.5%). In the national ranking it fell from #150,452 to #154,182.
What does the Census say about the background of Kilfoy?
Among Census respondents with the surname Kilfoy, the largest self-reported group is White at 89.3%. The next largest groups are Hispanic (5.8%) and American Indian/Alaska Native (1.9%). 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 Kilfoy in the 2020 Census, accounting for 89.3% (92 people in the source table).
What is the full ancestry breakdown?
Kilfoy appears across multiple self-reported groups in the Census data. The largest shares in the 2020 file are White (89.3%), Hispanic (5.8%), American Indian/Alaska Native (1.9%). 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 Kilfoy (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 Kilfoy mean?
An Anglicized form of the Irish Gaelic surname Ó Cilfeadha meaning descendant of the devotee. 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 Kilfoy (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 people have the surname Kilfoy?
HowManyOfMe.org, our sister site, answers that with the living-bearer count in one glance.