He turned himself in to officers Monday.
The girl told detectives she was assaulted in September when she was in Knight's care. Knight was living with the girl's mother at the time of the assault. The woman was recovering from serious injures sustained on her job.
The child became frightened of Knight and told her mother about the man's behavior. The mother then reported the crime to the sheriff's office.
Knight is being held under $75,000 bond.