"We can all recognize how much people sacrifice as state troopers for the safety of fellow citizens," NJ Attorney General Paula Dow said.
More than 3,000 fellow officers, the public he protected, Governor Christie, top law enforcement attended.
Troopers from across the nation, some from as far as California, Maine and Florida, all gathered around his grieving widow and his family at the church of St Veronica to say thank you and farewell.
"It's first a tremendous loss to the family, what we lose affects everyone," said Anthony Campos of the Newark Police Department.
Castellano was part of a manhunt last Sunday morning, along 195, after a woman from an abandoned car allegedly told police she was with a man who had a gun and he'd run into the woods.
The trooper was struck and killed by a passing car.
Later, 30-year old Diana Hoffman's story proved untrue.
She now faces charges related to the trooper's death.
Castellano is survived by his wife, a 4-year old daughter, and a 1-year-old son.
Parents in the community brought their children to see the tribute.
"I wanted to show the boys the brotherhood of the police," said Diane Reppy, a Howell resident.
After the service, many officers signed a tribute banner for Castellano, was the first New Jersey trooper since 2004 to die in the line of duty.