He will be sentenced later. Judge Paul Funderburk presided over the trial, which began Monday.
Stratton was indicted in February 2011 on accusations he had oral sex with the girl.
The girl, now almost 15, testified earlier this week. Prosecutors say the girl is mentally challenged with the mental abilities of a 6-year-old.
Assistant District Attorney Brian Neely is the lead prosecutor in the case.
Wednesday, Stratton's wife, Shirley, testified that her granddaughter never mentioned any inappropriate touching or actions by anyone, and that she believed the girl could have been coached by others or assaulted by someone other than her husband.