Ten Common Hallucinations in Genealogical AI
by Alvin Blackshear | Historian &
Researcher <ablackshear@gmail.com>
If you've started using AI tools to help build out your
family tree, you've probably noticed something exciting: AI can search
patterns, suggest connections, and summarize records faster than any human
researcher. But you may have also noticed something unsettling. Sometimes the
AI is simply wrong, and it's wrong with total confidence. It doesn't
hedge. It doesn't say "I'm not sure." It states fabricated facts as
if they were pulled straight from a courthouse archive.
This isn't a quirk specific to genealogy tools. It's a
well-documented feature of how large language models work. Researchers have
found that AI systems are, in a sense, rewarded for guessing rather than
admitting uncertainty, much like a student on a hard exam who writes down a
plausible-sounding answer rather than leaving the question blank. The same
dynamic that produces fabricated legal citations in court filings and
nonexistent references in academic papers also produces invented ancestors,
false marriages, and imaginary historical explanations in your family tree.
For beginning genealogists who are comfortable with AI tools
but new to the discipline of genealogical research, this creates a real risk.
Family history has its own standards of evidence (rules developed over
generations of professional practice), and AI, for all its fluency, doesn't
inherently know or follow them. Below are ten (plus a bonus eleventh)
hallucinations you're likely to encounter, along with how to spot each one.
#1. Invented Ancestors
The most obvious and probably most common hallucination is
the flat-out invented person. If your records show John Smith born in 1846,
married to Sarah Jones, and died in 1912, an AI tool may cheerfully add
"William Smith, father of John" to your tree, simply because a
father-shaped gap exists and the model has learned that fathers usually appear
in these slots.
No birth record names him. No probate record mentions him.
No document anywhere establishes his existence. He is, in the most literal
sense, a statistical guess dressed up as a fact.
How to catch it: Ask the AI directly, "What
specific document supports this person's existence?" If it can't name
one, or names one that turns out not to exist (see #5), strike the individual
from your tree.
#2. False Parentage
This is a subtler and more dangerous error because it
doesn't invent anyone; it just connects the right person to the wrong family.
Imagine two men named James Brown, both born in Virginia in 1818, but belonging
to two entirely unrelated families. An AI tool, pattern-matching on name,
place, and approximate date, may merge them, attaching one man's documented
parents to the other man's documented children.
Because online family trees copy from each other constantly,
an error like this doesn't stay contained. It can spread across dozens or
hundreds of public trees within months, becoming "true" simply
through repetition.
How to catch it: Whenever two individuals share a
name, county, and rough birth year, ask the AI to list the specific evidence
distinguishing them: land records, church parishes, associates named as
witnesses, distinguishing middle names. If it can't distinguish them, you
probably have two people, not one.
#3. Collapsing Two People into One
Related to false parentage, this hallucination happens when
the AI treats "same name, similar era, same county" as sufficient
proof of "same person." Common names are especially vulnerable: John
Williams, William Johnson, Mary Jones, Elizabeth Brown. In many rural
communities of the eighteenth and nineteenth centuries, several unrelated
people carried the same name at the same time.
How to catch it: Before accepting that two records
refer to one individual, ask what independent evidence (land transactions,
church membership, military service, or family testimony) ties them together,
not just shared name and geography.
#4. Splitting One Person into Several
The mirror-image error: one real person recorded
inconsistently, as "Robert," "Robt.," "Bob," and
"R.J.," gets treated by the AI as four different people. Suddenly
your family tree has artificially multiplied, with duplicate siblings or
duplicate spouses cluttering the record.
Nineteenth-century clerks were not consistent spellers, and
names were frequently abbreviated, translated, or anglicized. AI models,
trained to treat text strings literally, can miss the obvious inference that a
human researcher would make instantly.
How to catch it: When a "new" individual
appears with a name variant of someone already in your tree, in the same
location and timeframe, check whether the records could plausibly describe one
person before treating them as separate.
#5. Invented Sources
Perhaps the easiest hallucination to catch once you know to
look for it, and one of the most dangerous when you don't. AI tools will
sometimes cite a source that sounds entirely plausible: "County Probate
Book 14, page 327" or "Virginia Marriage Register, Volume 8."
The citation has the right shape, the right format, the right level of
specificity. It just doesn't exist.
This mirrors a broader, well-documented problem. A 2026
analysis of AI-generated academic writing found a sharp rise in nonexistent
references following widespread adoption of large language models, with a
conservative estimate of nearly 147,000 hallucinated citations appearing in
2025 alone. Similar patterns have shown up in legal filings, where courts have
caught lawyers submitting briefs built on cases that were never decided because
an AI tool invented them. Genealogy is not immune to the same failure mode; if
anything, it may be more vulnerable, since archival citation formats are
formulaic and easy for a model to imitate convincingly.
How to catch it: Never accept a citation at face
value. Look the source up yourself, in the actual archive, library catalog, or
online record collection, before recording it as fact. If you can't locate it,
assume it doesn't exist until proven otherwise.
#6. Imaginary Historical Context
AI loves to explain. "The family likely moved west
because of the Panic of 1837." It's a tidy, plausible sentence. It may
even be historically reasonable. But plausible is not the same as documented,
and an AI tool rarely marks the difference clearly. Historical interpretation,
offered without evidence specific to your family, quietly becomes historical
fiction wearing the authority of fact.
How to catch it: Treat any sentence containing words
like "likely," "probably," or "given
the context of the time" as a hypothesis to test, not a fact to
record. Ask what document (a land sale, a migration record, a letter) actually
supports the claimed motive.
#7. Overconfident Translation
If your ancestors left records in German, Polish, Latin,
French, or Dutch, AI translation can feel like a superpower, until it isn't. AI
models translate old church and civil records with impressive fluency, but that
fluency can mask serious errors: invented words to fill illegible gaps, misread
names, or entire phrases reconstructed from context rather than actually read.
Genealogists working with foreign-language parish records have reported AI
tools fabricating names, places, and even whole narrative details that don't
exist in the original document.
How to catch it: For any translation affecting a
name, date, or relationship, ask for a word-by-word rendering alongside the
smooth translation, and compare it against the original image yourself, or have
a human speaker of the language check ambiguous passages.
#8. Fabricated Relationships
A record lists a witness, Samuel Jones, at a wedding or a
will signing. The AI concludes he must be an uncle, brother, father, or cousin.
But witnesses in historical documents were frequently neighbors, business
associates, fellow church members, or simply friends, not relatives at all. The
AI's eagerness to complete the family picture leads it to assign a relationship
where the record specifies none.
How to catch it: Treat every unlabeled name in a
record (witness, executor, sponsor, bondsman) as a relationship of unknown type
until independent evidence establishes otherwise.
#9. Timeline Repair
Large language models dislike contradictions, and historical
records are full of them. If a record shows a birth in 1820 and a marriage in
1832, and something else nearby seems inconsistent, an AI tool may quietly
adjust one of the dates so everything appears internally consistent. The
apparent contradiction vanishes, but so does the actual historical evidence,
replaced by a smoothed-over fiction that fits the model's sense of what
"should" be true.
How to catch it: When a date changes between one AI
response and another, ask why, and check both figures against the original
record. Real historical records are often genuinely inconsistent, and that
inconsistency is itself information, not a bug to be silently fixed.
#10. Source Laundering
This is probably the least recognized hallucination, and
arguably the most insidious. AI tools trained on the vast ocean of
user-submitted online family trees absorb whatever errors already exist there,
including all the mistakes described above, made by human researchers over the
past two decades. The AI then presents those errors back to you as though they
were settled historical fact.
Nothing here is invented from scratch. That's what makes it
dangerous. The information already circulates online, attached to seemingly
credible trees and family history websites, so it carries an unearned
appearance of authority. The AI hasn't lied exactly; it has simply repeated
community folklore as though it were consensus.
How to catch it: Be especially skeptical of any claim
the AI attributes to "commonly accepted" genealogy or "widely
documented" family history. Ask what primary source underlies the claim,
not what other online trees say about it.
An Eleventh Hallucination: Certainty Inflation
There's one more pattern worth naming, even though it's
rarely discussed: certainty inflation. Professional genealogists are trained to
say, when the evidence doesn't fully support a conclusion, "the evidence
is insufficient." AI tools are much less comfortable with that kind of
humility. Instead, they tend to write things like "based on available
evidence, John was almost certainly the son of..."
That phrase, "almost certainly," can
represent an enormous leap well beyond what the underlying evidence supports.
This isn't accidental. Research into why language models hallucinate has found
that the training and evaluation processes used to build these systems reward
confident, plausible-sounding answers over honest expressions of uncertainty,
the AI equivalent of a student guessing on a test rather than leaving a blank.
The result is a model that is statistically inclined to sound more certain than
the facts warrant.
Toward a Genealogical AI Evaluation Framework
None of this means AI is useless for family history
research; far from it. It means AI output needs to be treated the way a careful
historian treats any single source: as a claim to be verified, not a fact to be
recorded.
One useful discipline is to treat every AI-generated
genealogical statement as a research hypothesis, never as evidence in itself.
Accept only what can be traced back to an identifiable primary or reliable
secondary source, and preserve uncertainty wherever the historical record
itself remains uncertain. In practice, that means running each AI claim through
a short mental checklist:
|
Criterion |
Key
Question |
|
Source
authenticity |
Is every
factual claim traceable to a real, locatable source? |
|
Evidence
chain |
Can the
conclusion be reconstructed from the cited evidence? |
|
Identity
confidence |
Has the AI
distinguished between similarly named individuals? |
|
Chronological
consistency |
Are dates
plausible without silent correction? |
|
Geographic plausibility |
Do locations
fit historical boundaries and migration patterns? |
|
Uncertainty
disclosure |
Does the AI
distinguish evidence from inference? |
|
Genealogical
Proof Standard alignment |
Would the
conclusion satisfy professional genealogical standards? |
Applying a framework like this won't eliminate hallucinations (no current AI
system is free of them), but it will keep you from mistaking a fluent,
confident answer for a well-documented one. AI can be a genuinely powerful
research assistant for genealogy: it can suggest search strategies, summarize
long documents, translate unfamiliar scripts, and spot patterns across large
record sets faster than any human could alone. Just remember that its job is to
help you find the evidence, not to become the evidence itself.
________________________________
Sources:
Kalai, Adam, et al. "Why Language Models Hallucinate." arXiv,
4 Sept. 2025, https://arxiv.org/abs/2509.04664.
Newsham, Jack. "AI Hallucinations in Court Documents
Are a Growing Problem, and Data Shows Lawyers Are Responsible for Many of the
Errors." Business Insider, 27 May 2026,
https://www.businessinsider.com/increasing-ai-hallucinations-fake-citations-court-records-data-2025-5.
Yin, Yian, et al. "LLM Hallucinations in the Wild: Large-Scale Evidence from Non-Existent Citations." arXiv, 8 May 2026, https://arxiv.org/abs/2605.07723.







