About 30 people attended the ceremony, including civil rights activist Rev. Jesse Jackson and several members of his Rainbow Push Coalition, CNN’s Omar Jimenez reported.
Day was reported missing on August 25 in Bloomington, Illinois, and his vehicle was found about an hour north in Peru, Illinois a day later.
An initial search on August 26 included Illinois State Police K-9 units, local jurisdictional aerial drone searches, and ground searches, but nothing was found, said Bloomington Police Department Officer John Fermon.
Authorities returned on September 4 following a lead and found the body, which would later be identified as Days floating in the Illinois River. The LaSalle County coroner said the cause of death was unknown pending further investigation.
The family also hired an independent private forensic pathologist to perform a second autopsy, but no results were released.
“I just saw one of the best things God has blessed me with sink into the ground and I will never speak to or see him again… I don’t even have the words to tell you how it is Day’s mother, Carmen Bolden Day, said after the funeral.
“I don’t know why I’m burying Jelani. I don’t know what happened to Jelani, so I have no closure,” said Bolden Day.
Day’s family criticized the authorities’ efforts on the case. “Jelani meant nothing to them,” Bolden Day told CNN last month.
“There is no effort. There is no pressure. There is nothing that has been done about my son.”
“Me and my kids, me and everyone who never knew Jelani – my family, friends, strangers – did all the leg work,” said Bolden Day. “My son didn’t get any help … He didn’t deserve it.”
Defending the investigation, Fermon said, “We’re lucky the story actually exploded that well, which may or may not have led to the tips received.” Fermon added that the search for Day 10 involved agencies and specialist teams in the Peru region, where the vehicle was found with assistance from the FBI.
Jackson also criticized the authorities’ response to Day’s case. “We won’t stop until it’s over,” he said.
Jackson called on the FBI and the US Department of Justice to “conduct a thorough investigation because it always smells like another case of Emmett Till,” he said in a statement, referring to the case of 14-year-old Till, who was murdered was born in Money, Mississippi, 1955.
Jackson said he was “obliged to help Mrs. Day,” noting that Till’s mother was holding an open-coffin funeral “so the world could see the terrible face of racism.”
Day’s mother said nothing in her son’s life that “would make you think he deserved to be found face down in a river”.
Day was studying speech therapy, according to his mother, who said he was “sociable, smart. He loves to have fun. He is energetic. He is sweet and compassionate. He’s kind and caring, ”Jackson said.
CNN’s Carma Hassan, Dakin Andone and Amir Vera contributed to this report.