The Co Louth man killed in Quincy, Boston, on Tuesday was still a member of the Defence Forces at the time of his death and is entitled to a military funeral at the request of his family.
Mr Ronan Stewart (23), Dublin Road, Dundalk, had applied to leave the Army and was on pre-discharge leave at the time of the accident.
Yesterday evening his younger sister, Niamh, said: "We are devastated, our parents are devastated, I don't think it has hit us yet."
She flew home from London after being told of her brother's death just three weeks into his visit to the United States.
He was staying in Brighton, Boston, but working on site for a demolition company in Quincy when the accident happened. Yesterday afternoon Mr Stewart's sister, Clodagh (29), who had travelled to Boston to see him last Saturday, had to formally identify his body. She was too traumatised by what happened to telephone home, and a close family friend rang his family with the news.
"He was the only boy in the family. He was just after leaving the family. He was a private in Cathal Brugha barracks in Dublin but came home every weekend," said his sister, Niamh.
Mr Stewart grew up in Dundalk, and his father, Michael, is a vice-principal of O Fiaich College, a secondary school in the town.
The second man killed in the accident, Mr Shane McGettigan (21), was from Drumshanbo, Co Leitrim. He is survived by his parents, Charlie and Gretty, and his two sisters.
He was a prominent Co Leitrim senior footballer who played for the senior team late last June in the Connacht senior football championship against Galway. Shane was also a member of the Alan Gael's GAA Club.
The family was in a state of "shock and disbelief and utter sorrow", according to the chairman of Alan Gael's, Mr Leo Kenny. "It's just impossible to talk about it."
It was a severe blow to the community, he said, adding that the county was numbed and the shock had brought life to a standstill in Drumshanbo.
He described Shane as an "outstanding young man in the community, not only as an outstanding football prospect but in every way". He was a popular young man, friendly and outgoing, and was extremely dedicated to his local and county teams and was one of Leitrim's brightest prospects.
The two men killed in the accident did not know each other before meeting in Boston last month.