2000
#130,443
National surname rank
Recorded bearers 120
First available Census row
Per 100,000 0.04
Very Rare Last name
Killoy
An Irish surname derived from the Gaelic word "cillóg" meaning small church or chapel.
According to the 2020 US Census Bureau surname tables, roughly 151 Americans carry the last name Killoy. That puts it at #133,220 in the national surname ranking, appearing at a frequency of 0.04 per 100,000 people (about 1 in 2,269,896 residents).
This page is the full Name Census profile for the Killoy 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
151
1 in 2,269,896
Census rank
#133,220
2020 decennial data
Per 100,000
0.0
Frequency rate
Recorded bearers
132
very rare in the US
Popularity narrative
The Census Bureau recorded 132 bearers of the surname Killoy in its 2020 decennial surname file. At a rate of 0.04 per 100,000 residents, it holds the 133220th position in the national surname ranking.
Among Census respondents with the surname Killoy, the largest self-reported group is White at 99.2%. The next largest groups are Two or More Races (0.8%).
Origin
Meaning and origin of Killoy
The surname Killoy has its roots in Ireland, tracing back to the 12th century. It is believed to have originated from the Irish Gaelic words "cill" meaning church and "uaidh" meaning cave or cave-dwelling, suggesting a potential connection to monastic settlements or those living near church caves.
The earliest recorded instances of the name can be found in medieval Irish annals and manuscripts. In the Annals of Ulster, a reference is made to a "Gillacholmoc Ua Cellaig" in the year 1167, which is thought to be an early spelling variation of the name Killoy.
During the 13th century, the name appeared in several land records and charters, indicating the presence of Killoy families in various parts of Ireland. One notable mention is in the Pipe Roll of Cloyne from 1291, where a "William Kylloy" is listed as a tenant farmer.
The surname Killoy has also been associated with certain place names in Ireland, such as Killybegs in County Donegal, which is derived from the Irish "Cill Bheag" meaning "little church". This suggests that some Killoy families may have resided in or near areas with similar place name origins.
Throughout history, several individuals with the surname Killoy have made their mark. One of the earliest recorded was Seán Ó Cillóid, a 16th-century Irish poet and historian from County Galway. Another notable figure was Pádraig Ó Cillóid, a 17th-century Irish scholar and scribe who worked on preserving ancient Irish manuscripts.
In the 18th century, Niall Ó Cillóid was a prominent Irish composer and musician, known for his contributions to traditional Irish music. In the 19th century, Máire Ní Chillóid was a celebrated Irish poet and storyteller from County Mayo.
More recently, in the 20th century, Brendan Killoy was a renowned Irish artist and painter, born in 1916 in County Sligo, whose works captured the rugged landscapes and cultural heritage of Ireland.
Demographics
Ancestry and ethnicity for Killoy
Among Census respondents with the surname Killoy, the largest self-reported group is White at 99.2%. The next largest groups are Two or More Races (0.8%).
The bar chart below shows how Killoy 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 Killoy surname at the time of the 2020 Census, not any inherent property of the name itself.
- White99.2% · 131
- Two or more races0.8% · 1
Timeline
Historical Census data for Killoy
Killoy 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
#124,548
National surname rank
Recorded bearers 138
+18 bearers (+15.0%)
Per 100,000 0.05
Rank movement Up 5,895 places
2020
#133,220
National surname rank
Recorded bearers 132
-6 bearers (-4.3%)
Per 100,000 0.04
Rank movement Down 8,672 places
| Year | Rank | Count | Per 100K | Count change | Rank change |
|---|---|---|---|---|---|
| 2000 | #130,443 | 120 | 0.04 | First available Census row | First available Census row |
| 2010 | #124,548 | 138 | 0.05 | +18 bearers (+15.0%) | Up 5,895 places |
| 2020 | #133,220 | 132 | 0.04 | -6 bearers (-4.3%) | Down 8,672 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 Killoy 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 | #124,548 | #133,220 | -7.0% |
| Count | 138 | 132 | -4.3% |
| Per 100K | 0.05 | 0.04 | -11.7% |
Between the 2010 and 2020 Census, the number of Killoy bearers went from 138 to 132 (-4.3% change). The surname moved down 8,672 positions in the national ranking, going from #124,548 to #133,220.
FAQ
Killoy surname: questions and answers
How many people in the U.S. have the surname Killoy?
Name Census estimates that about 151 living Americans carry the surname Killoy. Using the current population baseline, that works out to roughly 1 in 2,269,896 residents.
How common is Killoy?
Killoy ranks #133,220 in the 2020 Census surname tables and is classified on this site as "Very Rare." The Census recorded the name at a frequency of 0.04 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 132 people with the surname Killoy. That is different from the site's living-bearer estimate (151), which projects the surname's present-day count by applying the Census frequency rate to the current U.S. population.
What does 0.04 per 100,000 actually mean?
It is the Census Bureau's normalized frequency measure. A rate of 0.04 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 Killoy.
Has Killoy become more or less common over time?
Between 2010 and 2020, the surname Killoy went from 138 recorded bearers to 132. That is a decrease of 6 (-4.3%). In the national ranking it fell from #124,548 to #133,220.
What does the Census say about the background of Killoy?
Among Census respondents with the surname Killoy, the largest self-reported group is White at 99.2%. The next largest groups are Two or More Races (0.8%). 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 Killoy in the 2020 Census, accounting for 99.2% (131 people in the source table).
What is the full ancestry breakdown?
Killoy appears across multiple self-reported groups in the Census data. The largest shares in the 2020 file are White (99.2%), Two or More Races (0.8%). 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 Killoy (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 Killoy mean?
An Irish surname derived from the Gaelic word "cillóg" meaning small church or chapel. 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 Killoy (0.04 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 Killoy?
HowManyOfMe.org, our sister site, answers that with the living-bearer count in one glance.