PORTLAND — One of Maine’s largest undeveloped islands and a smaller neighboring island, once considered for acquisition by Acadia National Park, go on the auction block next month.

Bids for 744 acres of Marshall Island and the 12-acre Little Marshall Island will be opened Aug. 14, and the minimum offer in the closed auction is $4.5 million, said Steven Dome, project director of the California-based Kennedy-Wilson Inc.

Records show that the properties were bought over the past four years for under $1 million.

Marshall Island Realty Trust paid $750,000 in 1987 and 1989 for the Marshall Island land — the majority of the 925-acre island — and bought Little Marshall Island in 1989 for $170,000, according to records filed with the Bureau of Taxation.

However, Dome said a recent appraisal of the island showed the land parcel is worth $7.56 million.

Appraiser John Pervear of Northeast Harbor confirmed that the price paid for the land was under $1 million, but said the property is worth more now because of its unique character and work done to put the land package together.