Group of about 1,100 islands, southeastern Alaska, U.S. Extending southward from Glacier Bay, the chief islands are Chichagof, Admiralty, Baranof, Kupreanof, Prince of Wales, and Revillagigedo. The chief towns are Sitka (on Baranof) and Ketchikan (on Revillagigedo). The islands are separated from the mainland by deep, narrow channels that form part of the Inside Passage. The archipelago's name, given in 1867, honours Tsar Alexander II.