The crime was committed on Saturday night, October 8, at around 11.30pm.
A garda spokesperson has confirmed that a number of males gained entry to the church via a rear window and proceeded to ransack the sacristy.
The gardaí do not yet have details of what was taken. Anyone who may have witnessed anything is asked to contact Portlaoise Garda Station on 05786 74100.
When contacted by the Leinster Express, parish priest of Stradbally Fr Sean Maher declined to comment.
The burglary comes less than three weeks after St Joseph’s Church in Mountmellick was robbed in broad daylight.