An off-duty Bronx police officer committed suicide at his Long Island home — the fourth NYPD cop to take his own life this month, law-enforcement sources told The Post Thursday.

Kevin Preiss, 53, was found dead inside his Hicksville house in Nassau County with a self-inflicted gunshot wound to the head around 9:50 p.m. Wednesday, police said.

Preiss, who was married with children, was pronounced dead at the scene, sources said. He was just three days away from his 25th anniversary of joining the force, according to sources.

The death marks the fourth NYPD suicide in June, the sixth department suicide so far this year and, according to Chief of Department Terence Monahan, the 101st police officer to take their life in the country this year.

“It’s something . . . everyone needs to talk about,” Monahan told reporters Thursday. “We have to be willing to talk, and more important we have to be able to listen.”

The mood was somber Thursday at the 50th Precinct station house where Preiss worked.

“He was a good guy. Just a really nice guy,” a veteran officer said of Preiss. “It’s so sad.”

Another cop, who noted how Preiss was soon set to retire, added, “It’s heartbreaking.”

A civilian employee at the precinct said “no one ever saw the signs” leading up to Preiss’ death.

“He was going to retire next year…And he was always talking about all of the things he was looking forward to doing when he retired,” the employee said. “I can’t make sense of it.”

Mayor de Blasio — in Miami for the Democratic presidential debates — called the suicide “incredibly troubling” and added that “we’ve never seen anything like this” in reference to the spate of police suicides.

De Blasio said he and Police Commissioner James O’Neill “are going to be putting a whole set of strategies out to try to make clear to every police officer and their families that help is always there — that if anyone is feeling overwhelmed that they can turn for help and we will be there.”

“This is very, very painful and our officers do so much, but we’ve got to find a way to get the message across in a different way and provide support in a different way,” the mayor said.

On June 14, Officer Mike Caddy, 29, was found inside a vehicle on Wilcox Street behind the 121st Precinct station house with a self-inflicted gunshot wound. Caddy, a domestic-violence officer, had seven years on the job.

On June 6, veteran homicide Detective Joe Calabrese, 58, was found on Brooklyn’s Plumb Beach, also the victim of a self-inflicted gunshot wound to the head.

The day before, Steven Silks, the revered deputy chief of Queens North, fatally shot himself in the head in an unmarked patrol car. He was rushed to Elmhurst Hospital but could not be saved.

Additional reporting by Stephanie Pagones, Julia Marsh and David Meyer