Books of condolences were opened at St Joseph’s Church in Galliagh and Holy Family Church in Ballymagroarty in Derry, a city numbed by the scale of the grief wreaked on the remaining family of those drowned.
Sean McGrotty, 46, died along with his two sons Mark, 12, and Evan, eight, their grandmother Ruth Daniels, 57, and her 14-year-old daughter Jodie Lee Daniels.
The only survivor was Mr McGrotty’s four-month-old baby girl Rionaghac-Ann.
Hero rescuer Davitt Walsh swam out into Buncrana harbour in north County Donegal on Sunday night in an effort to reach the six people trapped in a car that had slid off the slipway into Lough Swilly.
Mr McGrotty handed him his baby out the broken driver’s side window just moments before the Audi Q7 sank.
Before the Dail held a minute’s silence in their memory, Enda Kenny said he will never forget the chilling eyewitness accounts that have touched the entire island.
Acting Taoiseach Mr Kenny said the magnitude of the horror put everything else in perspective.
“Our hearts go out to them and what is a devastating impact on the lives of the extended family,” he said.
“We all know in our own lives the numbing grief that comes with the loss of a loved one.
“In these circumstances, however, this is a particular and deepest grief, that the tranquillity and beauty of a sunny spring Sunday was shattered by this tragedy.”
Mr Kenny added: “I will recall - as many people will - forever the words of (eyewitness) Francis Crawford in his description of what happened.
“And I admire the courage of Davitt Walsh, who rescued and saved the life of baby Rionaghac-Ann.
“When you try to consider the horrendous impact of what was happening as that vehicle skid towards the water...
“A father handing his own baby to the rescuer - to say ‘save our baby’ - this puts things into perspective and in context.”
Fianna Fail leader Micheal Martin described it as an unspeakable tragedy and trauma.
“The nation is truly shocked at the scale of that tragedy and its wider impact on the communities of Donegal and Derry,” he added.
Sinn Fein leader Gerry Adams said the thoughts and prayers of everyone are with the family.
Parish priest in Derry’s Ballymagroarty, where the victims lived, Father Paddy O’Kane, spent his day preparing for Thursday’s funeral as well as comforting the mother of the two little boys and the rescued baby, Louise James.
She was in Liverpool at a hen party when the five members of her family drowned.
Ms James told the priest she was “destroyed” and “lost” since the tragedy.
Father O’Kane said the only “little sliver of hope” was the survival of baby Rionaghac-Ann.
She is said to be in a stable condition at Letterkenny University Hospital.