A Buffalo Township man who repeatedly sexually assaulted a mentally retarded girl will spend up to two years in prison.

Burdette “Bud” Doerr, 72, pleaded guilty to four counts of statutory sexual assault, six counts of corruption of minors and two counts of indecent assault of a person with a mental disability.

He cried as Butler County Judge William Shaffer sentenced him in compliance with a plea arrangement made with the county district attorney’s office: 1-2 years in the county prison, followed by 12 years’ probation.

“I didn’t plan for this to happen. I don’t know why it happened ... why I did these things,” Doerr told the judge. “I’m very, very sorry.”

Court records say the 15-year-old victim gave investigators “very detailed accounts” about how Doerr had assaulted her between May and October 2011 at her home and at his home.

Initially, Doerr faced 54 counts of rape and other sexual offenses.

Defense attorney Jerry Cassady told the judge the plea agreement was “appropriate” because Doerr cooperated with the investigation.

The victim did not appear in court to see the sentencing. But Assistant District Attorney Mark Lope said the girl as well as the girl’s guardian, her grandmother, approved the plea agreement.

As part of his sentence, Doerr was ordered to stay away from the girl.

Court officials said before being sentenced, Doerr was evaluated by a member of the state’s Sexual Offender Assessment Board, who determined he does not meet the criteria to be deemed a sexually violent predator under the state’s Megan’s Law. Still, based on the nature of the charges, Doerr will be required to register his whereabouts with state police for the rest of his life.

Cassady told the judge that Doerr, who’s been described as “an avid churchgoer,” was accompanied by three supporters to the courtroom, including his wife. But, “we could have filled up the court room on his behalf,” Cassady said.