A follow-up investigation led to charges the man also raped one of his daughters and molested another.
In exchange for the pleas Thursday, charges of parental child abuse, third- and fourth-degree sex offenses, second-degree assault of both daughters, and attempted second-degree rape were dropped.
The man's name is being withheld to protect the identity of the victims, who now range in age from 15 to 23.
He is being held at the Washington County Detention Center to await completion of a pre-sentence investigation ordered by McDowell.
In the case of the younger daughter, she told police in August her father began assaulting her when she was 6 or 7 years old. She said he would try to have intercourse with her but was unable.
She said there were times when she was forced to perform oral sex on her father, police reports said.
She told police she didn't know until the interview with police that her siblings had also been abused.
In September, the eldest daughter, now 23, told police her father began molesting her when she was 10. She said he forced her to have sexual intercourse with him several times a week for more than two years, police reports said.
He told her never to tell, police reports said. And until her interview in September, she told police she never did.
The police report noted that when one child told the mother of the incidents, she allegedly told that child not to say anything because "it was family."