David L. Williams of Coatesville was convicted of eight Class A felony counts of child molestation, one B felony count of incest and three C felony counts of child molestation.
The 38-year-old faces up to 370 years in prison.
"This is the worst case I have seen in my 32 years of practice," Putnam County Prosecutor Tim Bookwalter said. "The victim was 6-8 years of age when this happened. It would have taken place between 90 and 180 times."
The three-day jury trial ended with one hour of deliberation by the jury. They returned with a guilty verdict on 12 of the 13 counts.
Accusations by the victim's mother and an Indiana State Police investigation revealed that over a three-year period, Williams engaged in various sex acts with the girl in his rural Coatesville home.
He was arrested and several pieces of evidence were seized from his home on Jan. 26, 2012.
The victim actually took the witness stand during the trial, a task praised by the prosecutor.
"Our victim was a very brave girl. She had to come forward against her own (relative)," Bookwalter said. "She's a terrific little girl, and we hope for the best for her in the future."
Williams also took the stand, claiming police coerced his confession and that he actually blacked out for part of the interview.
However the jury watched nearly two hours of police interviews in which Bookwalter said state police investigators were courteous to the accused man.
"I asked the jury if they thought the police nice-guyed him to death," Bookwalter said.
Sentencing is set for Thursday, Jan. 31 in Putnam Circuit Court.