Colorado ( (listen), other variants) is a state in the Mountain West subregion of the Western United States. It encompasses 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 the eighth most extensive and 21st most populous U.S. state. The 2020 United States census enumerated the population of Colorado at 5,773,714, an increase of 14.80% since the 2010 United States census.

The region has been inhabited by Native Americans for more than 13,000 years, with the Lindenmeier site containing artifacts dating from approximately 9200 to 1000 BC; the eastern edge of the Rocky Mountains was a major migration route for early peoples who spread throughout the Americas. "Colorado" is the Spanish adjective meaning "ruddy", the color of red sandstone. The Territory of Colorado was organized on February 28, 1861, and on August 1, 1876, U.S. President Ulysses S. Grant signed Proclamation 230 admitting Colorado to the Union as the 38th state. Colorado is nicknamed the "Centennial State" because it became a state one century after the signing of the United States Declaration of Independence.

Colorado is bordered by Wyoming to the north, Nebraska to the northeast, Kansas to the east, Oklahoma to the southeast, New Mexico to the south, and Utah to the west, as well as touching Arizona to the southwest at the Four Corners. Colorado is noted for its vivid landscape of mountains, forests, high plains, mesas, canyons, plateaus, rivers, and desert lands. Colorado is one of the Mountain States, and is a part of the western and southwestern United States.

Denver is the capital of and most populous city in Colorado. Residents of the state are known as Coloradans, although the antiquated "Coloradoan" is occasionally used. Colorado is a comparatively wealthy state, ranking eighth in household income in 2016, and 11th in per capita income in 2010. It also ranks highly in the nation's standard of living index. Major parts of the economy include government and defense, mining, agriculture, tourism, and increasingly other kinds of manufacturing. With increasing temperatures and decreasing water availability, Colorado's agriculture, forestry, and tourism economies are expected to be heavily affected by climate change.