Colorado is a state in the United States encompassing most of the Southern Rocky Mountains as well as the northeastern portion of the Colorado Plateau and the western edge of the Great Plains. Colorado is part of the Western United States, the Southwestern United States, and the Mountain States. Colorado is the 8th most extensive and the 22nd most populous of the 50 United States. The United States Census Bureau estimates that the population of Colorado was 5,456,574 on July 1, 2015, an increase of 8.50% since the 2010 United States Census.