Three men, a woman and a child have been found in a container in a haulage yard.
The group of five, including the girl believed to be as young as three, were discovered in the depot of a transport company in New Ross, Co Wexford, on Sunday evening.
Gardaí said they are in good health and are being detained under immigration legislation with the case referred to the Refugee Applications Commission.
It is believed the group were brought into Ireland on the Irish Ferries Oscar Wilde ship which docked at Rosslare.
The five, believed to be Kurdish, told gardaí they were fleeing persecution and are looking for asylum in Ireland.