Colorado is a U.S. state 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 5,187,582 on July 1, 2012, an increase of +3.15% since the 2010 United States Census.
The state was named for the Colorado River, which early Spanish explorers named the Río Colorado for the red colored (Spanish: colorado) silt the river carried from the mountains. On August 1, 1876, U.S. President Ulysses S. Grant signed a proclamation admitting Colorado as the 38th state. Colorado is nicknamed the "Centennial State" because it was admitted to the Union in 1876, the centennial year of the United States Declaration of Independence.