A state police news release says the “consensual sexual relationship” went on from December 6 of 2012 to May 12 of last year. He retired as sheriff in July.
Mason, who is 52 years old, is also accused of providing alcohol to the girl.
State police say the accusations came to light during investigation of an unrelated civil matter.
Carlson heard the case because of Mason’s relationships with the McKean County district judges.