The Cambria County coroner says 43-year-old William Gephart died Thursday evening at Conemaugh Memorial Medical Center in Johnstown, where he has been treated since the crash on April 13.
The (Somerset) Daily American ( http://bit.ly/13yEXFd) reports Gephart was an officer in Paint Township, near Windber, about 65 miles east of Pittsburgh.
Authorities say he was riding the ATV with his young son when they were thrown from the vehicle after sideswiping a tree near the family's cottage in New Paris.
Gephart wasn't wearing a helmet, but his son was and the boy was treated for his injuries and released that night.
Information from: Daily American, http://www.dailyamerican.com