How Common Is the Last Name Oneill?
An estimated 56,608 people in the United States share the surname Oneill. That's about 1 in 6,055 Americans. This data comes from the 2020 U.S. Census Bureau surname frequency tables.
This page covers the Oneill surname's frequency in the U.S. population, its rank among all American surnames, and a breakdown of ancestry and ethnicity data from the Census. You can also check how many people share any first + last name combination involving Oneill.
Estimated Americans with this Surname
56,608
About 1 in 6,055 people in the U.S.
Census Rank
#673
Frequency Rate
16.52
per 100,000 people
Census Count
49,365
2020 Census
Data Source
2020
U.S. Census Bureau
Ancestry and Ethnicity for Oneill
The Oneill surname is most commonly associated with people who identify as White (89.84%). The next largest groups are Hispanic (5.20%) and Two or More Races (2.76%).
Self-reported race and ethnicity from the 2020 U.S. Census Bureau surname tables. Some categories may be suppressed for privacy when sample sizes are small.
Historical Census Data for Oneill
Oneill appears in 3 published Census surname releases on this site (2000, 2010, 2020). From 2000 to 2020, the raw count became more common and the per-100,000 rate became less common. Its best published rank was #633 in 2000.
Between the 2010 and 2020 census releases, the surname Oneill became less common in the United States. Both the raw count and the population-adjusted frequency moved down.
The line to watch most closely is per 100,000 people. That adjusts for overall population growth, so it shows whether Oneill became a bigger or smaller share of the country, not just whether the raw count went up.
Census Count Over Time
Raw Census count in each published surname release.
48,656 to 50,028
Per 100,000 Over Time
Population-adjusted frequency, which is usually the cleaner trend line.
16.52 to 18.04
Release-by-release summary
Each row is a published Census surname table for Oneill. The change column compares each release to the one before it.
| Year | Rank | Count | Per 100K | Change vs prior release | Largest recorded group |
|---|---|---|---|---|---|
| 2000 | #633 | 48,656 | 18.04 | Baseline release | White (94.28%) |
| 2010 | #689 | 50,028 | 16.96 |
Count 2.78%
Rate -6.17% | White (92.67%) |
| 2020 Latest | #673 | 49,365 | 16.52 |
Count -1.33%
Rate -2.65% | White (89.84%) |
If the raw count rose but the per-100,000 number fell, the surname still became less common relative to the size of the U.S. population. That is why the frequency rate usually tells the clearer story.
Recorded ancestry change
These percentages show how the Census profile for this surname shifted across the published surveys on this site.
| Ancestry | 2020 | 2010 | 2000 | Change Since 2000 |
|---|---|---|---|---|
| White | 89.84% | 92.67% | 94.28% | -4.83% |
| Black | 1.05% | 0.94% | 1.01% | 4.20% |
| Asian and Pacific Islander | 0.92% | 0.77% | 0.54% | 51.82% |
| American Indian and Alaska Native | 0.23% | 0.27% | 0.22% | 3.97% |
| Two or More Races | 2.76% | 1.36% | 1.20% | 78.82% |
| Hispanic | 5.20% | 3.99% | 2.75% | 61.67% |
These percentages come from self-reported Census data. They describe how the recorded makeup of people using the surname Oneill changed from 2000 through 2020, not the deeper family origin of every bearer of the name.
First Name + Oneill Combinations
How many people share a full name with Oneill as the last name? Click a combination below to see the estimate, or search any pairing.
Oneill Surname: Questions and Answers
How common is the last name Oneill?
Oneill is the #673 most common surname in the United States, with an estimated 56,608 people sharing this last name. It appears at a rate of 16.52 per 100,000 Americans.
Has the surname Oneill become more or less common over time?
In the published Census surname tables on this site, Oneill moved from 48,656 people in 2000 to 49,365 in 2020. The more important line is the population-adjusted rate, which changed from 18.04 to 16.52 per 100,000.
Why can the raw count go up while the rate per 100,000 goes down?
Because the total U.S. population can grow faster than the surname itself. A surname can have more people in absolute numbers but still make up a smaller share of the country, which is why the per-100,000 figure often tells the clearer story.
What does the ancestry change table show for Oneill?
It compares the published Census demographic mix for Oneill across releases on this page. That helps you see whether the recorded share of the surname shifted between groups over time, but it still does not tell the full family history of every person with the name.
What does 16.52 per 100,000 mean?
It means that if you picked 100,000 people in the United States at random, about 16.52 of them would have the surname Oneill. This is usually the clearest way to compare surnames because it adjusts for the size of the total population.
What ethnicity is the surname Oneill?
The Oneill surname is most commonly associated with people who identify as White (89.84%). The next largest groups are Hispanic (5.20%) and Two or More Races (2.76%). This data comes from the 2020 U.S. Census Bureau surname tables, which include self-reported race and ethnicity breakdowns.
Does the ancestry table tell the exact family origin of everyone named Oneill?
No. It shows how people with the surname Oneill identified in the Census. That is useful context, but it does not prove the deeper family history, nationality, or origin story of every person with the name.
How many people named [First Name] Oneill are there?
We can estimate any first + last name combination. Popular examples: Michael Oneill, James Oneill, John Oneill. Search any combination on our homepage.
Where does this surname data come from?
Surname frequency data comes from the 2020 U.S. Census Bureau decennial surname tables. These list every surname appearing in the Census along with frequency rates and demographic breakdowns. Full methodology.
Search for a full name combination
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