A 20-year-old Kent State University student was also shot. She was treated for her injuries and released from the hospital.
Latoya Williams said her son "was a good kid on the path to success."
Williams pleaded with parents and other people who were at the party to come forward with any details about the night of her son's death.
"Anybody with any information, please come forward and do the right thing," said Williams. "And I really want to reach out to the parents today from another mom. If you know your child went to this party, sit down and talk to them again and just beg and plea with them to do the right thing."
Tillman was majoring in political science at Eastern Michigan University and was involved in many organizations during college, according to his mother.
Authorities said a $2,500 reward will be offered for information in the shooting.
Police said there were 300-400 people at the party. Williams said she is frustrated about how little answers she has received about the events that led to her son's death.
"There were too many people there not to see something," Williams said.
Watch the full press conference in the media player above.