2000
#3,389
National surname rank
Recorded bearers 9,661
First available Census row
Per 100,000 3.58
Uncommon Last name
Moriarty
Anglicized form of the Irish surname Ó Muircheartaigh, meaning "descendant of Muircheartach," derived from muir meaning "sea" and ceardach meaning "skilled."
According to the 2020 US Census Bureau surname tables, roughly 11,181 Americans carry the last name Moriarty. That puts it at #3,567 in the national surname ranking, appearing at a frequency of 3.26 per 100,000 people (about 1 in 30,655 residents).
This page is the full Name Census profile for the Moriarty 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 Moriarty with 1881 census detail, origin facts and modern UK distribution where available.
Bearers in the US
11K
1 in 30,655
Census rank
#3,567
2020 decennial data
Per 100,000
3.3
Frequency rate
Recorded bearers
9.8K
uncommon in the US
Popularity narrative
The Census Bureau recorded 9,750 bearers of the surname Moriarty in its 2020 decennial surname file. At a rate of 3.26 per 100,000 residents, it holds the 3567th position in the national surname ranking.
Among Census respondents with the surname Moriarty, the largest self-reported group is White at 92.8%. The next largest groups are Hispanic (3.3%) and Two or More Races (2.4%).
Origin
Meaning and origin of Moriarty
The surname Moriarty originates from Ireland, with its earliest recorded use dating back to the 12th century. It is derived from the Gaelic name "Muircheartach," which means "navigator" or "skilled seafarer." The name reflects the maritime heritage of the Moriarty clan, who were prominent in coastal regions of Ireland.
The Moriarty family was initially concentrated in the counties of Kerry, Cork, and Limerick, where they held significant landholdings and positions of influence. The name is closely associated with the Dingle Peninsula in County Kerry, a region renowned for its seafaring traditions.
One of the earliest recorded instances of the Moriarty name can be found in the Annals of Inisfallen, a chronicle of Irish history dating back to the 12th century. The Annals mention several Moriarty clan members, including Muircheartach Ua Muircheartaigh, who was a prominent chieftain in the mid-12th century.
In the 16th century, the Moriarty clan played a significant role in the Desmond Rebellions against English rule in Ireland. Notable figures from this period include Donal Moriarty, a rebel leader who fought alongside the Earl of Desmond, and Muircheartach Moriarty, a prominent landowner and military commander.
Over the centuries, the Moriarty name has been associated with several notable individuals. One of the most famous was John Moriarty (1938-2007), an Irish writer and philosopher known for his influential works on mysticism and the human condition.
Other notable Moriartys include Edna Moriarty (1923-2021), an Irish stage and screen actress who had a prolific career spanning over seven decades, and Michael Moriarty (born 1941), an American actor best known for his roles in films like "Bang the Drum Slowly" and the TV series "Law & Order."
In fiction, the name Moriarty is perhaps most famously associated with Professor James Moriarty, the brilliant and villainous adversary of Sherlock Holmes in the works of Sir Arthur Conan Doyle. This fictional character has become an iconic figure in the Sherlock Holmes mythology.
While the Moriarty surname has its roots firmly in Ireland, it has since spread to various parts of the world due to immigration and diaspora. However, the name's connection to its Irish heritage and the legacy of the seafaring Moriarty clan remains strong.
Demographics
Ancestry and ethnicity for Moriarty
Among Census respondents with the surname Moriarty, the largest self-reported group is White at 92.8%. The next largest groups are Hispanic (3.3%) and Two or More Races (2.4%).
The bar chart below shows how Moriarty 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 Moriarty surname at the time of the 2020 Census, not any inherent property of the name itself.
- White92.8% · 9,051
- Hispanic or Latino3.3% · 321
- Two or more races2.4% · 235
- Asian and Pacific Islander0.8% · 81
- Black or African American0.4% · 42
- American Indian and Alaska Native0.2% · 20
Timeline
Historical Census data for Moriarty
Moriarty 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
#3,564
National surname rank
Recorded bearers 10,005
+344 bearers (+3.6%)
Per 100,000 3.39
Rank movement Down 175 places
2020
#3,567
National surname rank
Recorded bearers 9,750
-255 bearers (-2.5%)
Per 100,000 3.26
Rank movement Down 3 places
| Year | Rank | Count | Per 100K | Count change | Rank change |
|---|---|---|---|---|---|
| 2000 | #3,389 | 9,661 | 3.58 | First available Census row | First available Census row |
| 2010 | #3,564 | 10,005 | 3.39 | +344 bearers (+3.6%) | Down 175 places |
| 2020 | #3,567 | 9,750 | 3.26 | -255 bearers (-2.5%) | Down 3 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 Moriarty 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 | #3,564 | #3,567 | -0.1% |
| Count | 10,005 | 9,750 | -2.5% |
| Per 100K | 3.39 | 3.26 | -3.8% |
Between the 2010 and 2020 Census, the number of Moriarty bearers went from 10,005 to 9,750 (-2.5% change). The surname moved down 3 positions in the national ranking, going from #3,564 to #3,567.
Notable bearers
Famous people with the surname Moriarty
FAQ
Moriarty surname: questions and answers
How many people in the U.S. have the surname Moriarty?
Name Census estimates that about 11,181 living Americans carry the surname Moriarty. Using the current population baseline, that works out to roughly 1 in 30,655 residents.
How common is Moriarty?
Moriarty ranks #3,567 in the 2020 Census surname tables and is classified on this site as "Uncommon." The Census recorded the name at a frequency of 3.26 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 9,750 people with the surname Moriarty. That is different from the site's living-bearer estimate (11,181), which projects the surname's present-day count by applying the Census frequency rate to the current U.S. population.
What does 3.26 per 100,000 actually mean?
It is the Census Bureau's normalized frequency measure. A rate of 3.26 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 Moriarty.
Has Moriarty become more or less common over time?
Between 2010 and 2020, the surname Moriarty went from 10,005 recorded bearers to 9,750. That is a decrease of 255 (-2.5%). In the national ranking it fell from #3,564 to #3,567.
What does the Census say about the background of Moriarty?
Among Census respondents with the surname Moriarty, the largest self-reported group is White at 92.8%. The next largest groups are Hispanic (3.3%) and Two or More Races (2.4%). 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 Moriarty in the 2020 Census, accounting for 92.8% (9,051 people in the source table).
What is the full ancestry breakdown?
Moriarty appears across multiple self-reported groups in the Census data. The largest shares in the 2020 file are White (92.8%), Hispanic (3.3%), Two or More Races (2.4%). 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 Moriarty (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 Moriarty mean?
Anglicized form of the Irish surname Ó Muircheartaigh, meaning "descendant of Muircheartach," derived from muir meaning "sea" and ceardach meaning "skilled." 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 Moriarty (3.26 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 common is the surname Moriarty?
For a quick modern take, check how common the surname Moriarty is on our sister site HowManyOfMe.org.