Glennallen is a census-designated place (CDP) in the Copper River Census Area in the Unorganized Borough of the U.S. state of Alaska. As of the 2020 census, the population of the CDP was 439, down from 483 in 2010. It is the most populated community in the census area.

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.