Authorities say Matthew Nix had been living with the 15-year-old and having consensual sex with her. State law prohibits people 19 or older from having sex with anyone under 16 years old.
Nix told investigators that he thought the girl was 19. The girl says she told Nix she was 15.
In March, Nix pleaded no contest to sexual assault of a minor and possession of child pornography.
At his sentencing this week Nix was given two-to-four years for the sex assault, one-to-two years for the pornography, to be served at the same time. With time off for good behavior Nix could be released in a year and a half.