Admiralty Island is an island in the Alexander Archipelago in Southeast Alaska, at 57°44′N 134°20′W. It is 145 km (90 mi) long and 56 km (35 mi) wide with an area of 4,264.1 km2 (1,646.4 sq mi), making it the seventh-largest island in the United States and the 132nd largest island in the world. It is one of the ABC islands in Alaska. The island is nearly cut in two by the Seymour Canal; to its east is the long, narrow Glass Peninsula. Most of Admiralty Island—955,747 acres (3,868 km2)—is protected as the Admiralty Island National Monument administered by the Tongass National Forest. The Kootznoowoo Wilderness encompasses vast stands of old-growth temperate rainforest. These forests provide some of the best habitat available to species such as brown bears, bald eagles, and Sitka black-tailed deer.

The Alexander Archipelago is a 300-mile (480 km) long archipelago in North America lying off the southeastern coast of Alaska. It contains about 1,100 islands, the tops of submerged coastal mountains that rise steeply from the Pacific Ocean. Deep channels and fjords separate the islands and cut them off from the mainland. The islands shelter the northern part of the Inside Passage as it winds its way among them.