Boo! came a day late, but the name stuck anyway, the New York Daily News reported Sunday.
"We didn't want to call her 'it' while she was in utero, so we called her 'Boo' because of Halloween," said Drew Elliott, Boo!'s father.
The exclamation point was added to Boo!'s name later to make sure people knew her name was related to Halloween, the newspaper said.
"It was the joke that became reality," Boo!'s mother, Erika, said. "I love the exclamation point. 'Boo' is wimpy without it ... and Halloween now is extra fun."
The child's name wasn't too popular at the beginning, the parents said. Erika Elliott's mother "hated it," and Drew Elliott's father accused him of condemning his daughter to years of abuse at school.
But the name did have some unexpected benefits.
"Nobody ever forgets her name, and all of her (preschool) classmates learned what an exclamation point is," said Boo!'s father.
And Boo!, who removed the exclamation point for a few months during the first grade, likes her name.
"I took it off in first grade because I was embarrassed about it, but now I like it," said Boo!. "It's something to show off."