Montague Island, Alaska, is at the mouth of Prince William Sound on the southern shore of Alaska . It's actually quite large. Its longest axis is about 50 miles. Montague Straight is located between the island and the mainland. There is another large island to the north of Montague Island, named Hinchinbrook Island, and the gap between the two islands (and thus the entrance to Prince William Sound) is named Hinchinbrook Entrance. The highest point on Montague Island is named Montague Peak (elevat0on 658 feet).