NJ Transit and Glen Rock police responded about a half-mile south of the Main Line train station shortly before 2:30 a.m., borough Police Chief Dean Ackermann said.
They found the victim in a wooded area near the Route 208 overpass, he said.
Official identification was pending of the man, believed to be in his late 20s to early 30s, who was pronounced dead at the scene.
No injuries to the crew or 10 riders aboard the train were reported, NJ Transit said.
The No. 1101 Main Line train left Hoboken at 1:32 a.m. and was scheduled to arrive in Suffern at 2:42 a.m., the agency said.
"There was no disruption of service as this was the last train of the night," said NJ Transit, which was leading the investigation.
Glen Rock firefighters and paramedics from the Valley Hospital in Ridgewood assisted.
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