The State of Colorado is a state in the Rocky Mountain region of the United States of America. Colorado may also be considered to be a part of the Mountain, Southwestern, and Central regions of the United States. The United States Census Bureau estimates that the state population was 4,753,377 in 2006, a 10.49% increase since U.S. Census 2000. Denver is the capital and the most populous city of Colorado. Citizens of Colorado are known as Coloradans.