The North Shore Land Alliance has purchased a 28-acre Mill Neck residential property for conservation, the Old Westbury-based organization announced Monday.

The estate had been owned by the Humes family and will be incorporated into adjacent conservation areas called the Shu Swamp Preserve and Francis Pond. Alliance president Lisa Ott said the acquisition will create 120 acres of connected habitat in an important watershed.

"It's huge for water resources," Ott said in an interview Monday. "It's an extremely sensitive and important conservation area -- and people will be able to walk there."

The property includes meadowland, woodland, wetlands and nine residential structures.

The sale of the property for $5.2 million was announced in December but didn't close until Friday in part because several underground oil tanks had to be removed, Ott said.

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The nonprofit organization was able to buy the property with a combination of loans from The Conservation Fund, a Virginia-based nonprofit, an anonymous donor and $3 million from fundraising. Ott said additional fundraising is needed to repay the loans and for future expenses on the property.

A large house on the property includes historical features dating back more than 100 years, but is in dire need of repair, Ott said. "The core of the house is salvageable and could be fabulous," she said.

If the alliance is unable to raise at least $2.5 million of additional funds officials may need "to sell off some of the less important structures on the perimeter," Ott said.

The property is not yet open to the public. A committee will meet to develop a plan for the property, including whether to preserve or demolish the residential buildings, she said.

The alliance has played a role in the preservation of more than 1,000 acres of land on Long Island since it was founded in 2003, according to its website.