Fr. Bill Langlois told the congregation at St. Patrick - St. Anthony on Sunday the man admitted taking the cash over a lengthy time period.
He was fired immediately, and the police were notified.
Church officials also handed over their financial records to the police for review, in compliance with policy from the Catholic diocese.
"This announcement was the most difficult message I have ever had to make to the congregation. I delivered the same message at four liturgies and each time it was more painful," Fr. Langlois said.
"I know that the parish is hurt, they feel betrayed. We will all be grieving together, but with the Good Lord's help, we will rise above this matter. While the behavior cannot be condoned, we must establish a spirit of forgiveness and seek reconciliation."