About 150 people are expected to attend the reunion from throughout New Zealand as well as Australia, Ireland, and England.
Co-ordinator Roger Hardie, of Auckland, said he never forgot his Central Otago roots and the reunion was about celebrating the voyage made from Northern Ireland to New Zealand by William John Millar.
Mr Millar, who was a prominent figure in Naseby from 1863 until his death in 1900, founded the Millar family and associated branches of family in the Maniototo.
He built and owned the Eweburn Hotel and had a large land-holding in and around Naseby, and was one of the family's many descendants buried in the Naseby Cemetery.
His wife Margaret was also buried there.
Mr Hardie said there were eight branches of the family stemming from Mr Millar, seven of which would be represented by descendants at the reunion.
No members of the eighth family branch were alive, he said.
"Three of my four ancestral lines are represented in the Naseby Cemetery. My heart belongs to Central Otago," he said.
Mr Hardie said Mr Millar travelled to New Zealand with two of his children, leaving one behind in Ireland.
Although Mr Hardie and his family did not know the reasoning behind the decision, he said the granddaughter of the son who stayed in Ireland would attend the reunion.
"I think it was to placate the grandparents, with the hope they would reconnect again later on. It's quite sad, because Mr Millar never saw his son again," Mr Hardie said.
Reunion members converged on Naseby yesterday for an informal social gathering.
Today a family member who had researched the family's history will tell the group about his findings, after which members will be assisted by four local volunteers who have agreed to help navigate a walking history tour of the village.
Tomorrow the group will visit the site of Mr Millar's former hotel at the now non-existent Eweburn village, near the junction of State Highway 85 and Naseby-Ranfurly Rd.
"The Eweburn Hotel he built and owned had 22 rooms, so it was quite big. There was a Eweburn school opposite which, from memory, catered for about 35 children, so there must have been quite a village there at one stage" Mr Hardie said.
He said support from the Naseby community towards the reunion had been tremendous, and despite it being such a large group, people had been warm and welcoming.
"For people who come from a metropolitan area, it's really nice to be in touch with the warmth and fellowship of a small community town. We really appreciate it," he said.
