Chicago Mayor Richard Daley and the Rev. Jesse Jackson were among those who spoke at the three-hour service for Darnell Hudson Donerson, 57, Jason Hudson, 29, and Julian King, 7.
The three were found shot to death late last month, the adults in Donerson's home and Julian in a vehicle found several miles away. Julian is the son of Jennifer Hudson's older sister, Julia Hudson.
No one has been charged in the shootings, although authorities have called Julia Hudson's estranged husband, 27-year-old William Balfour, a "person of interest." He remains in custody on a parole violation.
During the service, "American Idol" winner Fantasia Barrino sang the gospel song "Your Grace and Mercy," and at one point left the stage to take Jennifer Hudson's hand and sing directly to her, the Chicago Tribune reported.
Small blue tickets that read "Hudson Family Funeral" were needed to enter the massive Apostolic Church of God, but that didn't deter crowds of onlookers who gathered outside.
Glover Lewis, who lives in the same South Side neighborhood as the Hudson family, attended the services and told the Tribune he was touched by the way Hudson bid her family members goodbye.
"Jennifer is the pillar," Lewis said. "It's obvious she's holding the family together."
Shenika Bowers, 35, of Chicago was one of several dozen people who stood outside the church in hopes of sharing sympathies with the singer-actress.
"She needs us right now," Bowers said of Hudson. "She needs support from everyone who she can get it from. I cannot imagine how she feels but I do feel for her."
Latosha Funches, 33, of Chicago, said she's been a Hudson fan since the singer was on "American Idol" and wanted to pass along her condolences.
"I have kids of my own too," said Funches, who pushed her 11-month-old son in a stroller. "I know how she feels. I just hope she can get through it. She looks like she's very strong."
Jennifer Hudson was a finalist in the 2004 season of "American Idol" and she won her Oscar in 2007 for her film debut, a supporting role in "Dreamgirls."
Monday's services followed a public memorial held Sunday at Pleasant Gift Memorial Baptist Church, where Hudson sang in her childhood.
The bodies of Donerson and Jason Hudson were discovered Oct. 24 at the family's home. Julian's body was found three days later in a sport utility vehicle on the city's West Side.
Police arrested Balfour the same day the bodies of Donerson and Hudson were discovered. After 48 hours - the longest Chicago police can hold a person without charges - Balfour was taken by the Illinois Department of Corrections on a parole violation.
Balfour had served seven years for a 1999 attempted murder and vehicular hijacking conviction.
His mother, Michelle Balfour, of Chicago, has denied that her son had anything to do with the deaths.