The 22-year-old exchange student suffered injuries after apparently diving from a pier at North Avenue Beach into shallow waters in Lake Michigan in the early hours of Thursday morning.
His parents, Yvonne and Liam, who flew out from Ireland at the weekend, were at his bedside when he passed away at Northwestern Memorial Hospital in Chicago, shortly after 6 p.m. on Saturday.
A friend who was with him at the time he entered the waters of the lake, tried to rescue him and raised the alarm. The emergency services, both firefighters and police, were quickly on the scene.
Galway City councilor, Terry O’Flaherty, said it was very tragic for the family and friends of the young man and she extended her heartfelt sympathy to them.
It is understood O’Reilly was in the U.S. on a J1 visa and working for the summer at a hotel in Chicago. He was among a group of about 30 irish students who are doing summer work in the city. Some of the shocked young students kept vigil in the hospital after the accident.
A postmortem was being carried on Sunday and arrangements were being made to bring O’Reilly’s body home to Ireland.