The services, held at St. Patrick's Roman Catholic Church in the hamlet of Bedford, took place on a beautiful spring morning, three days after Kennedy, 52, was found dead of an apparent suicide at her nearby estate.
Guests arriving for the service included prominent members of the Kennedy family and celebrity friends like comedians Larry David, Dan Aykroyd and Chevy Chase, actor Edward James Olmos and tennis great John McEnroe.
The casket was carried into the church by a group that included three of Mary Kennedy's older children and one of her sisters.
Kennedy's sister-in-law and nearly lifelong friend, Kerry Kennedy, told reporters gathered outside the church that she was "brilliant, and she was beautiful, and she cared so very, very deeply about everybody around her."
She said that Kennedy battled depression and mental illness for many years, but loved her children deeply. Only Tuesday, she said, she was talking about where her daughter, Kyra, would go to school.
"Mary was an angel," she said, her voice breaking.
Mary Richardson married into the Kennedy family in 1994, but had been close to the clan since meeting Kerry at boarding school as a teenager. She had four children with Robert, the son of assassinated U.S. senator and Attorney General Robert Kennedy, but the couple separated years ago. He filed for divorce in 2010. The case was pending when she died.
Shortly after the split, her internal struggles became public when she was arrested twice on charges of driving while intoxicated.
The domestic turmoil extended into preparations for her funeral. One of Mary's brothers went to court to request custody of her body, which could potentially have spoiled a Kennedy plan to bury her near the family's seaside compound in Hyannisport, Mass.
Robert Kennedy and a lawyer for the Richardson family spent part of the day in court Friday arguing the case, before Mary's body was released to her husband just hours before her planned wake. Details of the case were sealed by a judge.