2000
#7,068
National surname rank
Recorded bearers 4,363
First available Census row
Per 100,000 1.62
Rare Last name
Kilby
Derived from a place name meaning "farm by a spring" in Old English.
According to the 2020 US Census Bureau surname tables, roughly 4,757 Americans carry the last name Kilby. That puts it at #7,694 in the national surname ranking, appearing at a frequency of 1.39 per 100,000 people (about 1 in 72,053 residents).
This page is the full Name Census profile for the Kilby 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 Kilby with 1881 census detail, origin facts and modern UK distribution where available.
Bearers in the US
4.8K
1 in 72,053
Census rank
#7,694
2020 decennial data
Per 100,000
1.4
Frequency rate
Recorded bearers
4.1K
rare in the US
Popularity narrative
The Census Bureau recorded 4,148 bearers of the surname Kilby in its 2020 decennial surname file. At a rate of 1.39 per 100,000 residents, it holds the 7694th position in the national surname ranking.
Among Census respondents with the surname Kilby, the largest self-reported group is White at 86.6%. The next largest groups are Black (5.4%) and Two or More Races (4.0%).
Origin
Meaning and origin of Kilby
The surname Kilby is of English origin, originating in the northern counties of England during the medieval period. It is derived from the Old English words "cyll" meaning a small stream or brook, and "by" meaning a farmstead or settlement. Therefore, the name likely referred to someone who lived near a small stream or brook.
The earliest known record of the name Kilby dates back to the 12th century in the Pipe Rolls of Lincolnshire, where it is spelled as "Killeby." This indicates that the name was already established in this region during the Norman period. In the 13th century, the name appears in various spellings such as "Killebi" and "Killeby" in the Hundred Rolls of Oxfordshire and Warwickshire.
One of the earliest known bearers of the name was John Kilby, who was mentioned in the Subsidy Rolls of Yorkshire in 1301. Another early record is that of Thomas Kilby, who was listed in the Feet of Fines for Staffordshire in 1364. These historical records provide evidence of the name's widespread usage and various spellings during the Middle Ages.
In the 16th century, the name Kilby can be found in several parish records, such as the baptism of William Kilby in Fulbeck, Lincolnshire, in 1593. During this period, the name also appeared in association with various place names, such as Kilby in Leicestershire and Kilby Bridge in Yorkshire.
Among notable individuals with the surname Kilby throughout history are:
1. Richard Kilby (c. 1560-1639), an English clergyman and academic who served as the Regius Professor of Hebrew at the University of Oxford.
2. John Kilby (1711-1786), a British civil engineer and surveyor who contributed to the development of canals and waterways in England.
3. Jack Kilby (1923-2005), an American electrical engineer and inventor who is credited with the invention of the integrated circuit, for which he received the Nobel Prize in Physics in 2000.
4. Clyde L. Kilby (1902-1986), an American author, literary critic, and professor at Wheaton College, known for his works on C.S. Lewis and J.R.R. Tolkien.
5. Brendan Kilby (born 1981), an Australian rules football player who played for the West Coast Eagles and the Melbourne Football Club in the Australian Football League (AFL).
The surname Kilby has a rich historical lineage, originating from the northern counties of England and reflecting the geographic features of the areas where its earliest bearers lived. Its evolution over the centuries, with various spelling variations and associations with different locations, is a testament to the enduring legacy of this English surname.
Demographics
Ancestry and ethnicity for Kilby
Among Census respondents with the surname Kilby, the largest self-reported group is White at 86.6%. The next largest groups are Black (5.4%) and Two or More Races (4.0%).
The bar chart below shows how Kilby 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 Kilby surname at the time of the 2020 Census, not any inherent property of the name itself.
- White86.6% · 3,592
- Black or African American5.4% · 222
- Two or more races4.0% · 166
- Hispanic or Latino3.2% · 132
- Asian and Pacific Islander0.6% · 24
- American Indian and Alaska Native0.3% · 12
Timeline
Historical Census data for Kilby
Kilby 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
#7,534
National surname rank
Recorded bearers 4,412
+49 bearers (+1.1%)
Per 100,000 1.50
Rank movement Down 466 places
2020
#7,694
National surname rank
Recorded bearers 4,148
-264 bearers (-6.0%)
Per 100,000 1.39
Rank movement Down 160 places
| Year | Rank | Count | Per 100K | Count change | Rank change |
|---|---|---|---|---|---|
| 2000 | #7,068 | 4,363 | 1.62 | First available Census row | First available Census row |
| 2010 | #7,534 | 4,412 | 1.50 | +49 bearers (+1.1%) | Down 466 places |
| 2020 | #7,694 | 4,148 | 1.39 | -264 bearers (-6.0%) | Down 160 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 Kilby 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 | #7,534 | #7,694 | -2.1% |
| Count | 4,412 | 4,148 | -6.0% |
| Per 100K | 1.50 | 1.39 | -7.5% |
Between the 2010 and 2020 Census, the number of Kilby bearers went from 4,412 to 4,148 (-6.0% change). The surname moved down 160 positions in the national ranking, going from #7,534 to #7,694.
FAQ
Kilby surname: questions and answers
How many people in the U.S. have the surname Kilby?
Name Census estimates that about 4,757 living Americans carry the surname Kilby. Using the current population baseline, that works out to roughly 1 in 72,053 residents.
How common is Kilby?
Kilby ranks #7,694 in the 2020 Census surname tables and is classified on this site as "Rare." The Census recorded the name at a frequency of 1.39 per 100,000 residents, which is about 1 people out of every 100,000.
How many people with this surname were counted in the Census?
The raw 2020 Census file counted 4,148 people with the surname Kilby. That is different from the site's living-bearer estimate (4,757), which projects the surname's present-day count by applying the Census frequency rate to the current U.S. population.
What does 1.39 per 100,000 actually mean?
It is the Census Bureau's normalized frequency measure. A rate of 1.39 per 100,000 means that if you picked a random group of 100,000 U.S. residents, you would expect about 1 of them to have the surname Kilby.
Has Kilby become more or less common over time?
Between 2010 and 2020, the surname Kilby went from 4,412 recorded bearers to 4,148. That is a decrease of 264 (-6.0%). In the national ranking it fell from #7,534 to #7,694.
What does the Census say about the background of Kilby?
Among Census respondents with the surname Kilby, the largest self-reported group is White at 86.6%. The next largest groups are Black (5.4%) and Two or More Races (4.0%). 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 Kilby in the 2020 Census, accounting for 86.6% (3,592 people in the source table).
What is the full ancestry breakdown?
Kilby appears across multiple self-reported groups in the Census data. The largest shares in the 2020 file are White (86.6%), Black (5.4%), Two or More Races (4.0%). 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 Kilby (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 Kilby mean?
Derived from a place name meaning "farm by a spring" in Old English. 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 Kilby (1.39 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 Kilby?
For a quick modern take, check how many Americans have the surname Kilby on our sister site HowManyOfMe.org.