A representative from each family was asked to come forward and place a single white rose at the memorial outside Bessbrook Town Hall following an internominational service. It was attended by First Minister Arlene Foster, Justice Minister David Ford, UUP leader Mike Nesbitt and TUV leader Jim Allister.
Several hundred people, including relatives of the dead and the sole survivor, Alan Black, were present, as well as Michael Gallagher, whose son Aiden died in the 1998 Omagh bomb, and victims' campaigner Willie Frazer.
They came together to pay tribute to the sons, brothers, fathers and uncles who were killed as they returned from a day's work at Glenanne textile factory on January 5, 1976.
Their minibus was stopped and the gunmen singled out all the Protestants, allowing the one Catholic on board to run away before opening fire.
The victims were John Bryans; Robert Chambers; Reginald Chapman; Walter Chapman; Robert Freeburn; Joseph Lemmon; John McConville; James McWhirter, Robert Samuel Walker and Kenneth Worton.
Racquel Brush, who was only three when her father, 24-year-old Mr Worton, was killed, said: "You try not to get upset on a day like this, but it's hard because you think about the last 40 years and everything that has happened and the men weren't here to see it all.
"I was three and my sister was six, so I don't remember it.
"I don't remember my daddy either; you think you remember things, but it is probably just things family have told us. It's impossible to tell the difference between what you've been told and what you remember.
"I know my mummy told us it was bad men that did it and we were so young at the time we didn't really question it, but over the last couple of years an awful lot more has come out. There were people speculating at the time that it was revenge for what happened the night before (the killing of six Catholics in south Armagh), but it is obvious it was months in the planning.
"Mum was never the same, she never married again, she suffered bad health and we had to move away from Bessbrook because we lived next to the graveyard. We moved for her sanity.
"It's been great to see such a good turnout and people still remembering, although my aunt has just said to me that she remembers it like it was yesterday."
Mr Black, there with his only granddaughter Evie, said he was still haunted by the carnage.
Now 72, he was shot 18 times and spent months being treated for his devastating injuries.
He said: "Believe it or not, I am actually a private person. But I'm in that position where I feel I owe it to the men that died and their families to speak out."
Mr Black said he doesn't hold out much hope that those responsible will be brought to justice. "I don't know if it would help, I don't know how it would feel until it happens," he said.
Mr Gallagher, who has been an integral part of the campaign for truth about the Omagh bomb, laid a wreath at the memorial.
He said he understood the pain they felt during the service.
"Their lives took a very different direction than they would have, the majority of them would have gone on to have happy families and they were denied that.
"Everyone lost something that night."
The First Minister branded the massacre "one of the cruellest and cold-blooded acts of terrorism during the Troubles".
"I will stand with the families in their campaign for justice and will help them in any way I can."