Isabella Tolley, FDNY firefighter William Tolley’s 8-year-old daughter, sat inside a Bethpage church Thursday at her dad’s funeral, clutching a blanket emblazoned with his portrait.

Perched loosely atop Isabella’s head rested the navy blue dress-uniform helmet her dad would have worn if the solemn service inside St. Martin of Tours Roman Catholic Church was to remember someone else.

Her dad’s boss, FDNY Capt. Rich Blasi, of Ladder Company 135 in Ridgewood, Queens, approached the little girl and presented her with the helmet he wore exactly one week before on the day he died.

The captain’s gesture served as an unspoken message to a child left to grow up without a father: Isabella lost her dad that cool spring Queens afternoon but she will forever have a family in the fire department.

Legions of city firefighters made the trek to Bethpage Thursday, as did thousands more from Long Island and across the country. They were among the sea of sadness inside the church that included New York City Mayor Bill de Blasio and other city officials.

In his eulogy, de Blasio looked toward Isabella, sitting with her mother Marie, Tolley’s widow, and told her about losing his father young — an effort to offer her comfort.

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“You’ll wish you knew him better,” he said. “You’ll wish you had more time. But you’ll never have to wonder about his character — what he believed in, how he used his life on this earth.

The mayor called her father “a hero and it will sustain you.”

Fellow FDNY firefighter Jarrett Kotarski held back tears as he remembered Tolley’s passion for his job and devotion to his daughter.

“You were the best guy and the greatest fireman, and we’re going to miss you forever, brother,” he said in his eulogy.

Outside the church, de Blasio and his wife Chirlane McCray embraced Marie Tolley and Isabella.

Earlier, firefighters stood at attention, side by side in their dress uniforms, as the Ladder 135 truck carrying Tolley’s coffin and the rest of the funeral procession made its way to St. Martin of Tours. The procession was led by the ladder truck Tolley fell from when he plunged to his death.

Signs near the church said “God bless the FDNY” and “God Bless William Tolley.” Trees, signposts and telephone poles along the route were wrapped in red ribbons in Tolley’s honor.

Firefighters saluted Tolley and his family as the procession traveled along Central Avenue while the FDNY Emerald Society Pipes and Drums played “Amazing Grace.”

They saluted as Tolley’s coffin, draped with the FDNY flag, was lowered from a fire truck.

Nine firefighters led the coffin into the church. As the family walked in, the bagpipes and drums went silent. The firefighters ended their salute.

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Later, five helicopters — three from the NYPD, and one each from the Suffolk and Nassau police departments — buzzed low across the sky, passing above the church as the funeral procession prepared to leave.

When he was a kid growing up on Long Island, Tolley dreamed about becoming a firefighter and a rock star, his brother Robert Tolley said during the service. “As far back as I can remember, he had the little plastic mask and the little plastic oxygen tank.”

On the day his life ended, Tolley had achieved both dreams. He was a 14-year veteran of the FDNY and the drummer in a speed metal band, Internal Bleeding, that toured across the United States and Europe.

“He was a hard-core rocker and also a firefighter with a baby seat in the back of his minivan,” de Blasio said in his eulogy. “Talk about range.”

Other elected officials who attended Tolley’s funeral included Suffolk County Executive Steve Bellone, Nassau County Executive Edward Mangano, Nassau County Acting Police Commissioner Thomas Krumpter, City Councilwoman Elizabeth Crowley (D-Queens), city Public Advocate Letitia James and city Comptroller Scott Stringer.

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“It is inspiring to see thousands of New York City and Long Island firefighters,” Bellone said. “It is one big family that comes together in times of tragedy.”

Tolley had also served as a volunteer for the Bethpage and Hicksville fire departments.

“He will not be forgotten,” said Bethpage resident Joe Minogue, a retired FDNY member who led the department’s ceremonial unit. “He will never be forgotten by this community or the fire service.”

Robert Tolley, said his brother, “Billy,” wanted to be a firefighter “since he was 4 years old.”

“Any time that I spoke to my brother, not once was there any trepidation to go to work,” he told mourners. “We were best friends, we leaned on each other.”

He ended his eulogy by saying, “I love you, baby brother. Thank you all, today.”

The crowd gave him a standing ovation.

In his homily, Father Patrick Woods recalled a conversation Isabella had with her mother after Tolley died.

Isabella asked her mother why she had been gone all day, what was wrong.

“Marie, a loving mother, carrying her own crushing grief, tells her what happened,” Woods said.

The priest said that Isabella responded: “‘Mommy, Daddy’s too young to die.’ ”

Marie told her daughter: “Your daddy loved to help people. That’s what firemen do. And your daddy was a really good man at helping people.”