Monsignor William Lynn is serving three years after being convicted of endangering children in the archdiocese.
The Philadelphia Inquirer first reported that Lynn is at the Curran-Fromhold Correctional Center while he appeals his 2012 conviction.
It's not clear if he will still be there for the pope's September 27 visit or whether he would be among the inmates picked to meet with him.
Defense lawyer Thomas Bergstrom says Lynn would no doubt welcome the experience.