A portion of a prominent island in Casco Bay steeped in history is back on the market, only 10 months after a Florida real estate developer purchased the property.

The northeastern half of House Island was listed for sale by RE/MAX by the Bay on July 22. The asking price for the 13-acre lot, which includes three renovated cottages and a new boat dock, is $6.9 million.

The current owners of the property are Christina and Vincent “Cap” Mona, who operate Naples, Florida-based Three Palms Design Build LLC, a company formed in 2008 to remodel and rebuild homes, according to its website. The Monas purchased the property last October for $2.2 million, according to the Portland tax assessor’s database.

House Island sits in Casco Bay between Peaks Island and South Portland’s Spring Point, the site of Southern Maine Community College. In addition to its prominent place in Portland’s harbor, it also holds an important place in the city’s history.

An undated photo of House Island in the 1920s shows the “quarantine hospital,” doctor’s house and other structures. From an old postcard provided by Kim MacIsaac

Fort Scammell, built in 1808 and situated on the island’s southern tip, is the only fort along Maine’s coast to see action during the War of 1812, when it exchanged fire with a British privateer.

For much of the 1800s, two Portland fishing families used the island to cut, salt and dry groundfish, mostly cod. In 1905, the government bought the island to use as an immigration station.

The property was in the center of a historic preservation debate last year after Michael Scarks, a Portland developer, purchased the entire island with the intention of building luxury vacation homes while preserving limited public access to Fort Scammell.

Scarks bought the island in two stages. He purchased the northeastern half, which is now on the market, in May 2014 for $2.5 million. Two months later he purchased the other half of the island, which includes Fort Scammell, for $500,000, according to the tax assessor’s database.

After Scarks’ plans for luxury homes became public, historic preservationists began to worry about the potential loss or renovation of several structures on the island that were used by the federal government while operating the immigration center. Some locals call the island “the Ellis Island of the north.”

Portland’s Historic Preservation Board nominated the island to become a historic preservation district last August, after which Scarks sold the northeastern half of the island to the Monas. In January 2015, the Portland City Council approved the historic designation for the island.

Scarks died in March and attempts to reach the Monas were unsuccessful Friday. Vincent Mona told the city’s Historic Preservation Board in October that he and his wife were committed to spending the large sums needed to revive the historic structures on House Island and bring them up to code.

The listing agent for the property is David Banks of RE/MAX by the Bay. Attempts to reach Banks on Friday were not successful.