Dill does this because of the relationship (or lack thereof) with his father in real life.  In real life, Dill's parents do not seem to have much time for him.  They love him, but they do not spend time with him.

Because of this, you can see where he might want to compensate.  So he makes up all these stories about him and his father.  In the stories, they do all sorts of things together.  This makes it seem as if his dad really has a lot of time for him even though in real life he does not.

Dill lies as a way to feel wanted and included.

Charles Baker Harris is a little boy with a big imagination.  He comes to Maycomb to stay during the summer with his Aunt Rachel.  If you think about it, this is a bit of a red flag.  It means that there may be trouble in his home life. 

There is.  His father is absent.  We never get the full picture.  Stories about Dill’s father are almost always tall tales.

[He] said he had seen his father. Dill's father was taller than ours, he had a black beard (pointed), and was president of the L & N Railroad.  

"I helped the engineer for a while," said Dill, yawning.

"In a pig's ear you did, Dill. Hush," said Jem. (Ch. 4)

It is not hard to imagine why Dill would make up stories about his father.  He feels an emptiness there.  Notice that he compares his father to Atticus. He sees how Scout and Jem are with their father, and has a longing for the same kind of relationship. 

He wants Scout and Jem to admire him.  Most of Dill’s stories revolve around this kind of embellishment.

Dill Harris could tell the biggest ones I ever heard. Among other things, he had been up in a mail plane seventeen times, he had been to Nova Scotia, he had seen an elephant, and his granddaddy was Brigadier General Joe Wheeler and left him his sword.

"You all hush," said Jem. (Ch. 5)

Jem’s reaction to both stories is essentially the same.  He neither accepts nor disparages.  He pretty much deflects the story and moves on.  Jem is generally kind to Dill, and accepting of his whoppers.  Scout is more frustrated by them.  Scout says that “Dill had been studied and found acceptable” (Ch. 1) when they first meet him.  He is a boy, and even though he is younger than Jem, that makes him a hot commodity.  In some cases, this makes Scout feel left out though.

When Scout comes into her room one night to find him hiding under her bed, Dill comes up with his biggest story of all.  He explains that his mother remarried, and he had to run away from his wicked stepfather.  

Dill recited this narrative: having been bound in chains and left to die in the basement ... by his new father, who disliked him, and secretly kept alive on raw field peas by a passing farmer who heard his cries for help ..., Dill worked himself free by pulling the chains from the wall. (Ch. 14)

The incident is so serious that Dill does not even keep up the ruse for long.  He finally admits that "they just wasn't interested in me" (Ch. 14).  That is it in a nutshell for Dill.  All he wants is to be loved, and needed, and noticed.  The reason he tells his tales is so people will pay attention to him.  He ran away, back to Maycomb, because in Maycomb he feels loved.

You can tell that Lee really cares about the character of Dill.  There is no malice behind his lies.  His stories are designed to get people to listen to him longer, so that they pay attention to him.  Dill is a good storyteller. Maybe he will grow up to be a writer!

Look at mankind in general for your answer. Most people lie when the truth is not very attractive. Another reason for lying is to manipulate or get one's way. Out of the mouth of a young child like Dill, another reason to lie is simple creativity. Dill's purposes were probably mixed.

Dill's family situation is really untold in the book, but the book leads us to infer or believe that his situation was at least unstable. He was shifted around among relatives. Although Aunt Rachel probably had moments of true nurturing for Dill, what we see most in the text is her frustration with Dill. Dill's instability likely resulted in many misbehaviors because his parental structure was regularly changing.

I think Dill could get away with lies to the kids at least in the beginning because they didn't know his background. He chose good interesting things to lie about, and most kids want to impress other kids.

Dill says that his new father kept him chained to the wall in the basement and he broke free and escaped to Maycomb.

After a fight with Jem, Scout went upstairs to find what she thought was a snake under her bed.  It turned out to be Dill, who was not supposed to be in Maycomb.  In typical Dill fashion, he made up a giant whopper to explain why he was there and how he got there. 

Dill recited this narrative: having been bound in chains and left to die in the basement … by his new father, who disliked him, and secretly kept alive on raw field peas by a passing farmer who heard his cries for, … Dill worked himself free by pulling the chains from the wall. (Ch. 14) 

Dill said he paid for his way to Maycomb by traveling with a “small animal show” after being hired to wash the camel.  In reality, he stole money from his mother’s purse and took the train.  From Maycomb Junction he rode on the backboard of a cotton wagon.

Jem got Atticus, to Dill’s chagrin, who fed Dill and made sure his Aunt Rachel (and his mother) knew where he was.  Then when they went to bed Dill explained the real story to Scout.  He said that his new stepfather wasn’t “hateful,” but he just didn’t keep his promises.

“That wasn’t it, he—they just wasn’t interested in me.”

This was the weirdest reason for flight I had ever heard. “How come?”

“Well, they stayed gone all the time, and when they were home, even, they’d get off in a room by themselves.” (Ch. 14)

Dill had always wanted a father.  From the first time they met him, it was a sore spot with him.  He had high hopes for this one, but the new man in his mother's life was more interested in her than him.  Scout tells Dill that parents do not always do what they say, but Dill doesn't want a perfect parent.  He just wants to be wanted.

Scout accuses Dill of lying when he says that he has no father.

Dill is always telling stories, but the Finch children do not normally pay attention.  When Jem and Scout first meet Dill, he has a hard time explaining his family situation.

"I haven't got one."
"Is he dead?"
"No..."
"Then if he's not dead you've got one, haven't you?" (ch 1)

Dill does not want to admit that his father left, and his mother sent him away.  Dill’s home life is far from happy.  He makes up stories about how wonderful his father is, and the great things they do together, to hide the fact that he is in pain.

Despite Dill's whoppers, Scout and Jem enjoy his company and his stories.  They look forward to his summer visits.

In Harper Lee's To Kill a Mockingbird, Scout catches Dill lying about his father having a beard.

Dill is talking about how Boo must have a very long beard having been inside the house for so long. Scout mentions Dill's father's beard, and Dill replies that he doesn't have a beard. Scout reminds him of his story of his father with a beard, and though Dill makes excuses, Scout knows he telling "tall tales" (lies). She expects that the mounted police uniform he has spoken of will never show up either.

Dill Harris could tell the biggest ones I ever heard.

Scout then lists some of Dill's other lies. Dill says he's flown in a mail plane seventeen times, had traveled to Nova Scotia, had seen an elephant, and that his father was Brigadier General Joe Wheeler, who allegedly left Dill a sword. Dill doesn't have the home life that Scout and Jem do, and this may simply be his way of feeling more important rather than an outsider at home. Scout realizes that Dill tells stories, but doesn't seem to resent him for it.

Thoughts on Dill and Lying in "To Kill a Mockingbird"? In "To Kill a Mockingbird", why does Dill lie so much?  Why do you think this?

Sometimes Dill lies out of shame. He is ashamed about his family background. When Scout tries to pin Dill down about Dill's father, Dill says he has no father. Scout keeps pushing, asking if Dill's father is dead. Dill's reaction is to blush. At that point, Jem tells Scout to be quiet, essentially to leave Dill alone in regard to the subject of his family. Being older, Jem realizes that Dill is uncomfortable and embarrassed.

Dill knows that others suspect he isn't telling the truth.  They feign interest while they are calling home to check on him with his mother.  Dill also knows that while lying may get him a little more time in Maycomb, it won't keep him there since the Finchs don't make any room for those who are not in line with their idea of truth and justice.

Dill is a common young man suffering from neglect.  Although he has everything he needs to grow physically, he does not get much attention at home.  He is sent off in the summers to live with his aunt by a mother who does not show much interest in him.  He lies for two reasons:  1) he wants a better life than he believes he has; and 2) he wants attention.  He concocts stories to have others listen to him and show interest in him. 

When Dill runs away from home and hids under Scout's bed, this truth about him becomes clear.  He first lies and says that his new step-father abuses him.  If this lie is true, then Dill can stay in Maycomb, where he lives a better life and gets more attention.  Also, telling this story gets him both attention and concern from the adults.

However, Dill finally admits that this story isn't true.  He was simply angry that his mother seemed to have no time for him, and ran away to Maycomb in anger and looking for friends.

Like many children, Dill creates a larger-than-life father to make up for the obvious deficiences that the man exhibits. Throughout Harper Lee's novel To Kill a Mockingbird, Dill displays a knack for storytelling, and the tales about his father are among the biggest whoppers he tells. No doubt Dill feels neglected by both parents, who ship him off to his Aunt Rachel in Maycomb each summer instead of using the free time to spend with him as most parents would. Instead of admitting the awful truth to Jem and Scout, Dill creates fantastic stories that make the Finch children admire and envy him--at least some of the time.

... I asked Dill where his father was: "You ain't said anything about him."
    "I haven't got one."
    "Is he dead?"
    "No."
    "Then if he's not dead, you've got one, haven't you?"
    Dill blushed and Jem told me to hush, a sure sign that Dill had been studied and found acceptable.

Dill's fascination with Boo Radley only intensified Jem and Scout's own curiosity about Maycomb's mysterious ghoul. When he next returned, he now had a father

...taller than ours [with] a black beard (pointed) and was president of the L & N Railroad.

But by now, Jem and Scout knew him well:

    "I helped the engineer for a while," said Dill, yawning.
    "In a pig's ear you did, Dill. Hush," said Jem. "What'll we play today?"

Still later, Dill runs away from home, where Scout discovers him under her bed. Dill entertains his obviously enthralled pals with one of his greatest stories about

having been bound in chains and left to die in the basement by his new father, who disliked him...

But Scout suspected that no one could hate such a lovable fellow as Dill:

... "I said why'd you run off? Was he really hateful like you said?
    "Naw... they just wasn't interested in me."

Scout realized one big difference between Atticus and Dill's father: Atticus needed Scout. Dill believed his parents didn't need him. Their serious talk turned to Boo Radley once again, and Dill philosophized about why Boo had never run away.

"Maybe he doesn't have anywhere to run off to..."

Dill is lying so that he is able to stay in Maycomb. He admits that he ran away to Maycomb so that he was able to spend time with his friends. This is because he is not getting enough attention from his mother, so he is lying so that he will get attention. Dill also has a very active imagination, which contributes to his lying. He does not like the way that things are in his life, so he fabricates a better life for himself. We know that Dill is not receiving enough attention at home because he is sent away to spend every summer with his aunt.

At the outset of this story, Dill describes his father as having a long black beard. When the children begin playing and describing someone with a beard, Dill recants his statement, lying again and saying that his father had shaved it off "last summer." He also says that his father allowed him to help the conductors of a famous railroad, and that he had been sent money by him. None of the above are true.

Dill's reasons for lying boil down to the issue of attention: He is not affectionately tended to in the same way the Finch children are, and therefore feels the need to invent or justify his family's actions. And while Dill may not be as well-parented as the Finches, he does have a way with persuasion and imagination; Dill is the instigator of most of the mischief experienced by Jem and Scout, in fact. He is a friend, cohort, and fellow conspirator in most situations.

The lies that Dill tells are a way for him to cover up the reality of a not-so-great home life.  He states that he has an absentee father, which was probably very sad for him.  So, to make up for the lack of a father, he fills in that gap in his life with imaginative, more exciting possibilities.  One lie he tells about his father is that "he was president of the L&N Railroad", which is definitely an exciting position for a father to hold, if you are a little boy.  Later he claims that his father "was a lawyer like Atticus, only much younger."  This indicates that he longs for a father like Atticus; after spending so much time with the Finch family, he longs for a similar happiness.  But, he did put the convenient caviat that he was younger-a way to beat out Jem and Scout in the "my dad's cooler" contest.  When Dill runs away he claims that he had "been bound in chains and left to die in the basement...by his new father, who disliked him" but tells the more boring truth afterwards after Jem gets it out of him.  Perhaps Dill's mother is involved with a guy, and Dill doesn't like him, so he came up with that story, which is a highly entertaining one.

Dill's lying can be contributed to his love of adventure, thrill, novelty, and most importantly in some cases, to his longing for a more stable or loving home life.

Dill lies because he desperately wants to have a real family. Dill's father left, and it deeply affected him. Dill has a mother and no father, and the Finch children have a father and no mother. It is natural that the three children would find each other, since they are close in age and all similarly inquisitive and intelligent.

Scout and Jem know that Dill is making up everything he says about his father, and he knows that they know. The descriptions of his father are just part of the vivid fantasy life that all three children inhibit when Dill is in town.

For the narrative, Dill accomplishes a few things. First of all, he allows the children to explore Boo Radley's story because they introduce Dill to it. Second, he provides the children with opportunities to move the story along, including the night Jem left his pants at the Radley's house and during the trial. Dill's situation also adds to the theme of family explored throughout the book, because Dill's story line involves another unhappy family. When Dill's mother remarries, Dill feels left out and unloved, so he is able to return to the Finches, his true family.