Thieves crawled through a frozen drain and cut a hole in the surrounding fence to steal cigarettes and cash between 11pm on Monday night and 11am on Tuesday morning.
The thieves also disabled CCTV cameras, smashed a window and climbed through the roof causing thousands of pounds worth of damage to the 103-year-old club.
A Christmas dinner scheduled to take place on Tuesday night for 40 local senior citizens went ahead only due to the hard work of club committee members, according to chairman John Robinson.
"We had so many people in here working hard to get the place cleaned up and ready for the dinner. There was a gaping hole in the roof where they had kicked it in and bits of wood lying all over the bar," he said.
"It is so disappointing to know that people would do this to a local club that is there to provide for the wider community, and especially just hours before our annual Christmas dinner for the older generation here in Maghery."
The club has been targeted by thieves in the past according to bar manager Joe Nugent, who was first to arrive on the scene on Tuesday.
"This is the first time we have had an attack like this in about 18 months now, since we had CCTV and alarms installed," he said.
"It is not just an attack on the club, it is an attack on the local community and the people who did it should be ashamed of themselves."
Police have urged anyone with any information to contact Portadown police at 0845 600 8000 or to call the anonymous Crimestoppers line on 0800 555 111.