Billy Joel has donated $500,000 and joined the high-powered effort to rebuild the Sag Harbor Cinema, which was damaged in a December fire.

Joel’s donation earned him the naming rights for the theater’s popcorn stand and pushed fundraising efforts up to about $2.25 million, said the Sag Harbor Partnership, a nonprofit dedicated to restoring the theater.

April Gornik, the nonprofit’s vice president, said Joel got involved after his friends in the area contacted him about the fundraising.

“We are deeply grateful because Billy Joel’s presence here in Sag Harbor has been ongoing and significant as long as I’ve been in Sag Harbor, which is since the ’80s,” Gornik said Wednesday, noting that Joel has been known to play piano at the American Hotel on Main Street “for the lucky few who have happened to be there.”

“We are thinking of this as his ongoing tribute to Sag Harbor and to the cinema and to the village we all love so much,” she said.

Although partnership representatives declined to disclose the amount Joel donated, the $500,000 cost of purchasing the popcorn stand naming rights is detailed on the group’s website.

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The cinema was damaged in a Dec. 16 fire that tore through part of Main Street and damaged four other buildings. The front of the theater was subsequently demolished, leaving a hole in the middle of the village’s downtown.

The Sag Harbor Partnership signed a contract on April 6 to buy the property from longtime owner Gerald Mallow. But for the deal to go through, the nonprofit must have $6 million — 75 percent of the $8 million asking price — in pledged donations by July 1. The group also plans to raise as much as $5 million more to rebuild the distinctive Art Deco facade and outfit the main theater with a new sound and projection system, as well as adding two smaller screening rooms.

Movie mogul Harvey Weinstein and famed director Martin Scorsese are also part of the fundraising effort, along with the group’s advisory board, which includes Oscar-winning dame Julie Andrews and Anne Chaisson, executive director of the Hamptons International Film Festival.

“For as long as I can remember, the Sag Harbor Cinema has stood as a beacon of culture on Long Island,” Scorsese said in a statement. “I hope people from all over the East End will join in this fight to save Sag Harbor’s center of culture.”

Andrews joined after her daughter, Emma Walton Hamilton, who lives in Sag Harbor and co-founded the Bay Street Theater, offered to help the partnership, Gornik said.

“There isn’t a day that goes by when we drive down Main Street and don’t feel this kick in the gut when we see this hole,” Walton Hamilton said. “It’s a constant reminder of what we lost.”

Walton Hamilton said that she and her husband, Stephen, have been “going through our address books” to find people to help, which is how her mom, who “spends the bulk of her time out here,” got involved.

“For her, all we had to say was, ‘Can you join the advisory board?’ She said, ‘Of course. It matters so much.’ She’s aware of how important the cinema is to the village.”

Joel has long appreciated the importance of the Sag Harbor Cinema. He paid tribute to the theater during his December concert at Madison Square Garden, saying, “Just wanted to say goodbye to the old Sag Harbor Cinema,” playing a bit of Ennio Morricone’s “Cinema Paradiso” before launching into “New York State of Mind.”

Christie Brinkley, Joel’s ex-wife, shares his fondness for the theater. The supermodel/actress still owns an old version of the Sag Harbor Cinema neon sign, which she purchased at auction years ago.

Nick Gazzolo, the Partnership’s president, said Joel “knows exactly how much the sign and the cinema mean to all of Main Street.”

“So many of his songs show his understanding of how much specific places mean to people, and we are so grateful that he agrees the Sag Harbor Cinema is a special place worth fighting for,” Gazzolo said in a statement.