The City of Unalaska is the main population center in the Aleutian Islands. The city is in the Aleutians West Census Area, a regional component of the Unorganized Borough in the U.S. state of Alaska. Unalaska is located on Unalaska Island and neighboring Amaknak Island in the Aleutian Islands off mainland Alaska. The population was 4,254 at the 2020 census, which is 81% of the entire Aleutians West Census Area. Unalaska is the second largest city in the Unorganized Borough, behind Bethel.

The Unorganized Borough is composed of the portions of the U.S. state of Alaska which are not contained in any of its 19 organized boroughs. While referred to as the "Unorganized Borough", it is not a borough itself, as it forgoes that level of government structure. It encompasses nearly half of Alaska's land area, 323,440 square miles (837,700 km2), and, as of the 2020 U.S. Census, it had a population of 77,157, which was 10.52% of the population of the state. The largest communities in the Unorganized Borough are the cities of Bethel, Unalaska, and Valdez.