2000
#4,433
National surname rank
Recorded bearers 7,394
First available Census row
Per 100,000 2.74
Rare Last name
Riordan
An Irish surname derived from the Gaelic Ó Ríoghbhardáin, meaning "descendant of Ríoghbhardán" (royal poet or bard).
According to the 2020 US Census Bureau surname tables, roughly 8,651 Americans carry the last name Riordan. That puts it at #4,565 in the national surname ranking, appearing at a frequency of 2.52 per 100,000 people (about 1 in 39,620 residents).
This page is the full Name Census profile for the Riordan 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 Riordan with 1881 census detail, origin facts and modern UK distribution where available.
Bearers in the US
8.7K
1 in 39,620
Census rank
#4,565
2020 decennial data
Per 100,000
2.5
Frequency rate
Recorded bearers
7.5K
rare in the US
Popularity narrative
The Census Bureau recorded 7,544 bearers of the surname Riordan in its 2020 decennial surname file. At a rate of 2.52 per 100,000 residents, it holds the 4565th position in the national surname ranking.
Among Census respondents with the surname Riordan, the largest self-reported group is White at 92.2%. The next largest groups are Hispanic (3.3%) and Two or More Races (2.9%).
Origin
Meaning and origin of Riordan
The surname Riordan is of Irish origin, having derived from the Gaelic name "Ó Riórdáin," which means "descendant of Riórdán." The name Riórdán itself is a diminutive form of the old Irish personal name Riórd, composed of the elements "rí" meaning "king" and "ard" meaning "high" or "noble."
Historically, the Riordan family hailed from County Cork in the province of Munster, Ireland. They were a prominent sept (branch of a clan) of the O'Callaghan family, who were lords of the territory known as Úibh Rathach, located near the town of Kilbrin. The earliest known record of the name Riordan appears in the Annals of Innisfallen, an Irish chronicle compiled in the 13th century, where a chieftain named Donogh O'Riordan is mentioned as having died in the year 1237.
In the 16th century, the Riordans are recorded as having held lands in the baronies of Muskerry and Duhallow in County Cork. One notable figure from this period is Donell Riordan, who was a wealthy landowner and chieftain of the Riordan sept in the late 1500s.
During the Irish Confederate Wars of the 1640s, several members of the Riordan family fought alongside the Catholic Confederates against the English Parliamentarian forces. One such individual was Dermot Riordan, who served as a captain in the Confederate army and was killed in battle in 1646.
In the late 17th century, after the Williamite War in Ireland, many Riordans were dispossessed of their lands and forced into exile or reduced to tenant farmers. One notable figure from this time was Edmond Riordan (1670-1740), a wealthy landowner and poet who wrote extensively in the Irish language.
Other notable individuals bearing the Riordan surname include:
1. Michael Riordan (1774-1858), an Irish-American soldier who fought in the War of 1812 and later became a prominent businessman in New York City.
2. Patrick Riordan (1841-1914), an Irish-born American prelate who served as the Archbishop of San Francisco from 1884 until his death.
3. Roger Riordan (1922-2006), an American chemist and pioneer in the field of nuclear magnetic resonance spectroscopy.
4. Tomás Riordan (1914-1998), an Irish Gaelic poet and writer who was a prominent figure in the Irish literary revival of the 20th century.
5. Micheal Riordan (born 1952), an Irish-American physicist and science writer, best known for his biographies of renowned scientists such as Enrico Fermi and Richard Feynman.
Demographics
Ancestry and ethnicity for Riordan
Among Census respondents with the surname Riordan, the largest self-reported group is White at 92.2%. The next largest groups are Hispanic (3.3%) and Two or More Races (2.9%).
The bar chart below shows how Riordan 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 Riordan surname at the time of the 2020 Census, not any inherent property of the name itself.
- White92.2% · 6,955
- Hispanic or Latino3.3% · 250
- Two or more races2.9% · 219
- Asian and Pacific Islander1.0% · 74
- Black or African American0.5% · 38
- American Indian and Alaska Native0.1% · 8
Timeline
Historical Census data for Riordan
Riordan 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
#4,515
National surname rank
Recorded bearers 7,848
+454 bearers (+6.1%)
Per 100,000 2.66
Rank movement Down 82 places
2020
#4,565
National surname rank
Recorded bearers 7,544
-304 bearers (-3.9%)
Per 100,000 2.52
Rank movement Down 50 places
| Year | Rank | Count | Per 100K | Count change | Rank change |
|---|---|---|---|---|---|
| 2000 | #4,433 | 7,394 | 2.74 | First available Census row | First available Census row |
| 2010 | #4,515 | 7,848 | 2.66 | +454 bearers (+6.1%) | Down 82 places |
| 2020 | #4,565 | 7,544 | 2.52 | -304 bearers (-3.9%) | Down 50 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 Riordan 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 | #4,515 | #4,565 | -1.1% |
| Count | 7,848 | 7,544 | -3.9% |
| Per 100K | 2.66 | 2.52 | -5.1% |
Between the 2010 and 2020 Census, the number of Riordan bearers went from 7,848 to 7,544 (-3.9% change). The surname moved down 50 positions in the national ranking, going from #4,515 to #4,565.
FAQ
Riordan surname: questions and answers
How many people in the U.S. have the surname Riordan?
Name Census estimates that about 8,651 living Americans carry the surname Riordan. Using the current population baseline, that works out to roughly 1 in 39,620 residents.
How common is Riordan?
Riordan ranks #4,565 in the 2020 Census surname tables and is classified on this site as "Rare." The Census recorded the name at a frequency of 2.52 per 100,000 residents, which is about 3 people out of every 100,000.
How many people with this surname were counted in the Census?
The raw 2020 Census file counted 7,544 people with the surname Riordan. That is different from the site's living-bearer estimate (8,651), which projects the surname's present-day count by applying the Census frequency rate to the current U.S. population.
What does 2.52 per 100,000 actually mean?
It is the Census Bureau's normalized frequency measure. A rate of 2.52 per 100,000 means that if you picked a random group of 100,000 U.S. residents, you would expect about 3 of them to have the surname Riordan.
Has Riordan become more or less common over time?
Between 2010 and 2020, the surname Riordan went from 7,848 recorded bearers to 7,544. That is a decrease of 304 (-3.9%). In the national ranking it fell from #4,515 to #4,565.
What does the Census say about the background of Riordan?
Among Census respondents with the surname Riordan, the largest self-reported group is White at 92.2%. The next largest groups are Hispanic (3.3%) and Two or More Races (2.9%). 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 Riordan in the 2020 Census, accounting for 92.2% (6,955 people in the source table).
What is the full ancestry breakdown?
Riordan appears across multiple self-reported groups in the Census data. The largest shares in the 2020 file are White (92.2%), Hispanic (3.3%), Two or More Races (2.9%). 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 Riordan (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 Riordan mean?
An Irish surname derived from the Gaelic Ó Ríoghbhardáin, meaning "descendant of Ríoghbhardán" (royal poet or bard). 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 Riordan (2.52 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 Riordan?
See how many people are called Riordan on HowManyOfMe.org, our sister site built around that single question.