Carrey was among about 300 people who attended the service at Our Lady of Fatima Church in the village of Cappawhite in County Tipperary, Ireland. The Irish Times reported
the church was packed "with extended family members and friends, neighbors and those who traveled long distances to say their final farewells."
Carrey helped carry the coffin from the church to a nearby cemetery.
White was found dead September 28
. She and Carrey had dated on and off since reportedly meeting in 2012.
"She was a truly kind and delicate Irish flower, too sensitive for this soil, to whom loving and being loved was all that sparkled," the actor said in a statement upon hearing of her death. "My heart goes out to her family and friends and to everyone who loved and cared about her. We have all been hit with a lightning bolt."
White, a hairstylist and beautician, was believed to have committed suicide. She was 30 years old.
The Rev. Tadhg Furlong, who presided over the service, paid tribute to her "strong-willed" personality.
"Cathriona's approach to life was to take on, to challenge the county, the country, the world," he said, according to The Irish Times. "Cathriona was a light to so many. Something of the light has gone out. Yet much remains. The light continues to shine. The light of love lives on; the love you had for Cathriona; the love she had for you."
Carrey posted a photo in remembrance.
"Love cannot be lost," he wrote.