James Leone, 51, must serve 5 years of supervised release after completing the sentence.
Under federal guidelines, Leone faced 63 to 78 months in prison after pleading guilty in January 2013 to accessing a computer with intent to view child porn.
At the sentencing in Central Islip federal court, U.S. District Judge Arthur Spatt called the graphic preteen videos and pictures that Leone had viewed "bad . . . awful."
Spatt doubted Leone would commit another crime, and noted that he had led an otherwise exemplary life and was receiving therapy, but said prison time was required as punishment and a deterrent to others.
"There was no justification for what I did," Leone told the judge before the sentence was imposed. He expressed remorse and said his actions have scarred him for life.
"I have spent the majority of my life protecting people . . ., protecting children," he said. "I betrayed a trust."
Eastern District prosecutor Allen Bode told Spatt that "everyone should know better," but especially Leone.
"He knew firsthand" about vulnerable children being victimized, Bode said.
Earlier in his career, Leone was a New York City parole officer and a child abuse investigator for the city's child welfare bureau, officials said.
Federal agents came across Leone while investigating people sharing child porn on the Internet, according to court papers.
Leone later admitted that he had been searching for "preteen hard-core" porn for about a year, but deleted anything he watched because he did not want his wife or child to see it, the papers said.
Leone resigned after his arrest in September 2012.
