The requiem mass was held at St Mary's Church on the Melmount Road.
The teenager who died in a water-filled quarry in County Tyrone is the third member of his extended family to die in a drowning tragedy.
The body of Rhys Jack was recovered from the disused quarry in the Backtown area of Strabane on Tuesday afternoon.
Parish priest, Father Michael Doherty, said both of the teenager's parents had lost family members through drowning.
His mother lost her five-year-old brother about 40 years ago, while his father's uncle drowned in recent years.
Father Doherty has been with members of the Jack family since the tragedy began to unfold on Monday evening.
The 17-year-old was in the quarry with three teenage friends when they fell into the water from a makeshift raft.
His three friends, who were later rescued, had frantically tried to save him.
Father Doherty told BBC Radio Ulster's Evening Extra programme that Rhys's parents, Elaine and Mark, identified his body at the quarry shortly after it was recovered by search teams.
He said: "They knew over the past day, or from about eight o'clock last night (20:00 BST) that although they would have liked to have thought there was a chance he would be still alive, they knew that he was gone and their hope was that the body would be found sooner rather than later."
The priest said that their "deep sadness" at losing their son was mixed with "relief".
He explained that the corpse of Elaine Jack's young brother had never been found, so they were relieved that Rhys's body had been recovered.
He also said it was his understanding that Mark Jack's uncle had drowned in the River Finn a number of years ago.
Father Doherty was the Jack family's parish priest and had baptised Rhys 17 years ago.
He was also a chaplain at the teenager's school.
The priest said the three friends who had tried to save Rhys were "traumatised and upset".
He described the atmosphere in Rhys's school as "subdued" and said staff had tried to make special arrangements for those taking exams.

Nonsuch Palace was painted by the Flemish artist Joris Hoefnagel in 1568.
Culture Minister Ed Vaizey has placed a temporary export bar on the watercolour in the hope a UK buyer can match the asking price of £1m.
"We have very few paintings of the palace so I really hope we can find a buyer to keep this masterpiece here in Britain," he said.
The piece is the oldest of six remaining depictions of the palace, considered to be one of the Renaissance period's most stunning buildings.
Nonsuch Palace - named because no other palace could equal it - was built in 1538 for the Tudor king to celebrate the birth of his first legitimate son and mark his 30th year on the throne,
It was intended to rival the opulent residences of French king Francis I.
In 1670 Charles II gave the palace to his mistress, Barbara Villiers, who began to dismantle and sell parts of the building to pay off gambling debts.
By 1690 the building had all but disappeared.
The painting went for auction in 2010 but failed to meet its reserve price of £1.2m.
The decision to defer the export licence follows a recommendation by the Reviewing Committee on the Export of Works of Art and Objects of Cultural Interest (RCEWA), administered by Arts Council England.
They made their recommendation on the grounds of its close association with our history and national life, its outstanding aesthetic importance and its outstanding significance for understanding the nature of English Renaissance architecture.
The decision on the export licence application for the watercolour will be deferred until 31 May.
The funeral mass has taken place of teenager Rhys Jack who drowned in a quarry in Strabane last week.
[NEXT_CONCEPT]
The earliest depiction of Henry VIII's "lost" palace in Surrey could leave the UK unless a buyer comes forward.