On Nov. 26, Montgomery County authorities charged Kerns, 66, of North Wales, with 19 counts including rape, sexual assault, tampering with evidence, and lying to authorities.
The arrest came after a county grand jury urged charges in a 23-page report that portrayed Kerns as a manipulative rapist who allegedly drugged and twice sexually assaulted a 51-year-old woman employed at his Lansdale law firm after an Oct. 25 office party.
Defense lawyer Brian J. McMonagle has said Kerns "vehemently denies" the allegations.
The Administrative Office of Pennsylvania Courts received a request Dec. 4 from Montgomery County Court to have an out-of-county judge take over for District Judge Robert M. Sobeck in district-level proceedings, state courts spokesman Art Heinz said.
The Doylestown Intelligencer reported that Sobeck, who presided over Kerns' Nov. 26 preliminary arraignment, asked to be recused from the case this month for reasons that have not been made public. Sobeck could not be reached for comment.
Pennsylvania Supreme Court Justice Ronald D. Castille approved Welsh's assignment Thursday, Heinz said.
Paperwork detailing the request was unavailable Tuesday. But Heinz said the process of appointing an out-of-county judge begins with a request from the originating county's president judge, who in this case is William J. Furber Jr. Furber could not be reached for comment.
Speculation about a criminal investigation of Kerns roiled political circles in the days leading up to his arrest. The whispers grew louder when he resigned from his Republican post Nov. 14.
Montgomery County District Attorney Risa Vetri Ferman, a Republican, initially referred the case to Attorney General Kathleen Kane, a Democrat. Kane's office said it could not pursue the case unless there was an established conflict of interest. Ferman said there was not.
Deputy District Attorney Samantha L.R. Cauffman is handling the case.
Marcel Groen, chairman of the Montgomery County Democratic Committee, said the Kerns case isn't about politics.
"It's a horrific, tragic, sad thing. . . . I don't intend to make it political," Groen said. "I have a lot of respect for Risa. If she felt there were a conflict, she would have recused herself."