Robert Kerns is charged with indecent assault of a person unconscious, indecent assault of a person substantially impaired, and other offenses.
The alleged incident happened on October 25th. The victim was an employee at Kerns' private law practice at the time.
Prosecutors say Kerns met with the victim and tricked her, giving her wine laced with the sleeping medication Ambien. They say he then sexually assaulted her both in his car and at her home after she passed out.
Court documents say the assaults were violent and that the victim suffered severe injuries as a result.
In detailing the alleged assault, Montgomery County District Attorney Risa Ferman said Kerns planned the entire assault in advance and tried to cover his tracks afterward. The charges against him include evidence tampering.
Ferman described the victim as "very courageous" in coming forward.
The incident was first reported to Upper Merion Police on October 31st, six days after it occurred. But Ferman said the victim took the unusual step of going to the hospital for testing immediately, before reporting the assault to police.
That allowed crucial evidence to be preserved, including traces of Ambien still in the victim's system, as well as DNA evidence linking Kerns to the assault, Ferman said.
Kerns was taken into custody Tuesday. He had no comment coming in and out of court.
Kerns will have to post $100,000 cash to get out on bail.
News of Kerns' arrest came less than two weeks after he resigned as the chairman of Montgomery County's Republican Committee amid reports that an investigation was underway.
At the time, the executive director of the committee said in a statement the committee had "no comment on media reports related to a possible criminal investigation of Mr. Kerns unrelated to his duties as chairman."
Kerns is a lawyer and a partner at Kerns, Pearlstine, Onorato and Hladi.
"Mr. Kerns vehemently denies these allegations. He maintains his innocence. We look forward to testing and defeating these accusations in the court of law and restoring his good name," Center City defense attorney Brian McMonagle said.
Sources said Kerns' last job as chairman of the Republican Committee was to call a special meeting for December 4th, when a new chairman will be selected.