Authorities believe her story, that she had been kidnapped and held as a sex slave for all that time, and forced to have a child with her captor.
The girl, now 19, had been reported missing more than two years ago.
During a raid Thursday on a house in Washington Park, Illinois , a baby was also found.
The suspect is identified by neighbors as a 25-year-old Washington Park man. He was arrested along with his mother.
Neighbors were stunned by the accusations.
"They seemed pleasant, very nice family," said neighbor Connie Hunt. "They were normal ... We didn't know anything that was going on."
According to police, the victim managed to escape and walked into a police station.
Charges are pending.