2000
#140,756
National surname rank
Recorded bearers 109
First available Census row
Per 100,000 0.04
Very Rare Last name
Iwamasa
A Japanese surname derived from the words "iwa" meaning rock and "masa" meaning true or genuine.
According to the 2020 US Census Bureau surname tables, roughly 128 Americans carry the last name Iwamasa. That puts it at #147,954 in the national surname ranking, appearing at a frequency of 0.04 per 100,000 people (about 1 in 2,677,768 residents).
This page is the full Name Census profile for the Iwamasa 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
128
1 in 2,677,768
Census rank
#147,954
2020 decennial data
Per 100,000
0.0
Frequency rate
Recorded bearers
112
very rare in the US
Popularity narrative
The Census Bureau recorded 112 bearers of the surname Iwamasa in its 2020 decennial surname file. At a rate of 0.04 per 100,000 residents, it holds the 147954th position in the national surname ranking.
Among Census respondents with the surname Iwamasa, the largest self-reported group is Asian/Pacific Islander at 87.5%. The next largest groups are Two or More Races (5.4%) and Hispanic (2.7%).
Origin
Meaning and origin of Iwamasa
The surname Iwamasa is of Japanese origin, with its roots tracing back to the Edo period (1603-1868) in Japan. The name is believed to have originated in the Kyushu region, particularly in the areas surrounding the city of Kumamoto.
The name Iwamasa is a combination of the Japanese words "iwa," meaning "rock" or "stone," and "masa," which is an archaic word referring to a person or individual. Together, the name Iwamasa can be interpreted as "rock person" or "stone person," potentially referring to someone who lived near or worked with stone or rock formations.
In historical records, the earliest known mention of the name Iwamasa dates back to the late 17th century, when a samurai warrior named Iwamasa Nobuyuki (1655-1722) served under the Hosokawa clan, a prominent feudal family in the Kumamoto region. Nobuyuki's descendants continued to carry the Iwamasa name throughout the Edo and Meiji periods.
Another notable figure with the Iwamasa surname was Iwamasa Michiharu (1780-1856), a scholar and poet who lived during the late Edo period. Michiharu's works focused on classical Japanese literature and poetry, and he was known for his contributions to the study of the Man'yōshū, one of the oldest existing collections of Japanese poetry.
In the early 20th century, Iwamasa Masaaki (1892-1968) gained recognition as a pioneering architect and urban planner. He was instrumental in the development of modern urban planning concepts in Japan and played a significant role in the reconstruction efforts following the Great Kanto Earthquake of 1923.
During the Meiji era (1868-1912), the Iwamasa family also had a presence in the world of finance and banking. Iwamasa Shoichi (1835-1905) was a prominent businessman and banker who founded the Iwamasa Bank, one of the earliest modern banking institutions in Japan.
Another notable figure was Iwamasa Toshiko (1915-1987), a renowned author and feminist activist. Her literary works often explored themes of gender equality and women's rights, and she was a vocal advocate for social and political reforms in Japan during the post-World War II era.
While the Iwamasa surname is not among the most common in Japan today, it has a rich history dating back to the Edo period and has been associated with various influential figures across different fields, including warfare, literature, architecture, finance, and social activism.
Demographics
Ancestry and ethnicity for Iwamasa
Among Census respondents with the surname Iwamasa, the largest self-reported group is Asian/Pacific Islander at 87.5%. The next largest groups are Two or More Races (5.4%) and Hispanic (2.7%).
The bar chart below shows how Iwamasa 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 Iwamasa surname at the time of the 2020 Census, not any inherent property of the name itself.
- Asian and Pacific Islander87.5% · 98
- Two or more races5.4% · 6
- Hispanic or Latino2.7% · 3
- White1.8% · 2
- Black or African American1.8% · 2
- American Indian and Alaska Native0.9% · 1
Timeline
Historical Census data for Iwamasa
Iwamasa 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
#147,253
National surname rank
Recorded bearers 112
+3 bearers (+2.8%)
Per 100,000 0.04
Rank movement Down 6,497 places
2020
#147,954
National surname rank
Recorded bearers 112
+0 bearers (+0.0%)
Per 100,000 0.04
Rank movement Down 701 places
| Year | Rank | Count | Per 100K | Count change | Rank change |
|---|---|---|---|---|---|
| 2000 | #140,756 | 109 | 0.04 | First available Census row | First available Census row |
| 2010 | #147,253 | 112 | 0.04 | +3 bearers (+2.8%) | Down 6,497 places |
| 2020 | #147,954 | 112 | 0.04 | +0 bearers (+0.0%) | Down 701 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 Iwamasa 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 | #147,253 | #147,954 | -0.5% |
| Count | 112 | 112 | 0.0% |
| Per 100K | 0.04 | 0.04 | -6.3% |
Between the 2010 and 2020 Census, the number of Iwamasa bearers went from 112 to 112 (+0.0% change). The surname moved down 701 positions in the national ranking, going from #147,253 to #147,954.
FAQ
Iwamasa surname: questions and answers
How many people in the U.S. have the surname Iwamasa?
Name Census estimates that about 128 living Americans carry the surname Iwamasa. Using the current population baseline, that works out to roughly 1 in 2,677,768 residents.
How common is Iwamasa?
Iwamasa ranks #147,954 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 112 people with the surname Iwamasa. That is different from the site's living-bearer estimate (128), 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 Iwamasa.
Has Iwamasa become more or less common over time?
Between 2010 and 2020, the surname Iwamasa went from 112 recorded bearers to 112. That is an increase of 0 (+0.0%). In the national ranking it fell from #147,253 to #147,954.
What does the Census say about the background of Iwamasa?
Among Census respondents with the surname Iwamasa, the largest self-reported group is Asian/Pacific Islander at 87.5%. The next largest groups are Two or More Races (5.4%) and Hispanic (2.7%). 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?
Asian/Pacific Islander is the largest self-reported group for the surname Iwamasa in the 2020 Census, accounting for 87.5% (98 people in the source table).
What is the full ancestry breakdown?
Iwamasa appears across multiple self-reported groups in the Census data. The largest shares in the 2020 file are Asian/Pacific Islander (87.5%), Two or More Races (5.4%), Hispanic (2.7%). 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 Iwamasa (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 Iwamasa mean?
A Japanese surname derived from the words "iwa" meaning rock and "masa" meaning true or genuine. 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 Iwamasa (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 last name Iwamasa?
Our sister site HowManyOfMe.org answers how many people have the surname Iwamasa at a glance, with the living-bearer count up front.