The McHenry County Coroner's Office said Magdalena Jablonska, 48, of Des Plaines suffered life-threatening injuries in a boat crash on the Fox near the 1800-block of South Fernwood Lane in McHenry.
Jablonska suffered blunt force injuries to her body and head, the coroner's office said.
An autopsy was performed Tuesday.
Richard Stevenson, 45, has been charged with reckless homicide and aggravated driving under the influence in the crash.
He's been detained as the case moves forward.
During the court hearing, prosecutors outlined a timeline of events leading up to Saturday's collision. They alleged Stevenson was operating a 30-foot pontoon boat under the influence of alcohol at 80 miles per hour before striking another boat on the river, killing one of two people on board.
Security footage from a home along the Fox River allegedly showed the pontoon Stevenson was driving Saturday afternoon. According to the family that provided the video, their cameras captured the pontoon traveling south on the river and then, about an hour and 45 minutes later, heading north. About a minute later, they said they heard the collision.
Another video, recorded as a child played on nearby swings, showed the pontoon passing by at 12:40 p.m., nearly two hours before the crash.
Prosecutors said Stevenson's pontoon entered a no-wake zone and struck the rear of a green Crownline boat. A woman seated in the passenger seat of the Crownline was driven over and decapitated, prosecutors said. Her husband was taken to a hospital.
According to prosecutors, the pontoon came to rest on a riverbank, where a witness on Riverside Drive found Stevenson. He was later taken to a hospital, where a blood draw allegedly showed a blood alcohol concentration of 0.20, which prosecutors said was 2.5 times the legal limit.
Prosecutors also said two other people were aboard Stevenson's boat. Although both left the scene Saturday, they were later interviewed by police. Prosecutors said both reported Stevenson had taken multiple shots of Fireball whiskey that day. One of the passengers told investigators Stevenson was traveling 80 miles per hour before the collision.
In arguing for detention, prosecutors highlighted Stevenson's history of traffic-related offenses. They cited a period between 1997 and 2005 that included three DUI arrests, four misdemeanor speeding offenses, three reckless driving offenses and fleeing and eluding police. Prosecutors also pointed to a 2023 misdemeanor speeding violation for driving 26 to 34 miles per hour over the speed limit.
Stevenson is scheduled to return to court on Aug. 5.