Atka Island is the largest island in the Andreanof Islands of the Aleutian Islands of Alaska. The island is 50 miles (80 km) east of Adak Island. It is 65 miles (105 km) long and 2–20 miles (3–30 km) wide with a land area of 404.6 square miles (1,048 km2), making it the 22nd largest island in the United States. The northeast of Atka Island contains the Korovin volcano which reaches a peak of 5,030 feet (1,533 m). Oglodak Island is located 3.4 miles off Cape Kigun, Atka's westernmost point.

The Aleutian Islands —also called the Aleut Islands, Aleutic Islands, or, before 1867, the Catherine Archipelago—are a chain of 14 main, larger volcanic islands and 55 smaller ones. Most of the Aleutian Islands belong to the U.S. state of Alaska, with the archipelago encompassing the Aleutians West Census Area and the Aleutians East Borough. The Commander Islands, located further to the west, belong to the Russian federal subject of Kamchatka Krai, of the Russian Far East. The islands form part of the Aleutian Arc of the Northern Pacific Ocean, and occupy a land area of 6,821 sq mi (17,666 km2) that extends westward roughly 1,200 mi (1,900 km) from the Alaskan Peninsula mainland, in the direction of the Kamchatka Peninsula; the archipelago acts as a border between the Bering Sea to the north and the Pacific Ocean to the south. Crossing longitude 180°, at which point east and west longitude end, the archipelago contains both the westernmost and easternmost parts of the United States, by longitude. The westernmost U.S. island, in real terms, however, is Attu Island, west of which runs the International Date Line. While nearly all of the archipelago is part of Alaska at the extreme western end, the small, geologically-related Commander Islands belong to Russia.