A New Hampshire developer has closed on the purchase of a huge former mill building on Saco Island, clearing way for its redevelopment into residential apartments and retail space, Saco’s mayor announced Thursday.

Chinburg Properties of Newmarket, New Hamphsire, is the new owner of Building Number 4, a four-story, 237,600-square-foot building at the gateway to Saco that has been empty for about 30 years, Mayor Donald Pilon said in a written announcement.

“This is a new day for what will be Saco’s biggest development project, and I’m happy that it will finally get to the finish line,” Pilon said in the news release.

The sale price of the building has not been disclosed. Pilon said Chinburg Properties plans to invest more than $18 million in renovations and create 140 units of market-priced housing and retail space.

The sale was closed on Wednesday and follows the Saco City Council’s approval on Monday of property tax incentives in the form of a Tax Increment Financing district.

The transfer of ownership takes place amid a rush of recent development news in the Biddeford and Saco downtown mill districts.