The St. Lawrence County Sheriff's office identified the man as 45-year old Kevin Seig of Potsdam.
According to a media release, the Sheriff's office got a call at 10 p-m Sunday about an accident off Sissinville Road. Deputies found Seig on the track bed with severe head and internal injuries. He had been struck by a CSX locomotive, and was airlifted to Syracuse.
The cause of the accident is under investigation.