Colorado is called the Centennial State because it became a state in 1876, during the United States' centennial celebration. Although "Centennial State" is Colorado's official nickname, it also has other nicknames. It has been called "Colorful Colorado," a nickname that the state government has used on license plates, signs and promotional material. Colorado's rich mineral deposits have led to the alternate nicknames "Silver State" and "Lead State," its high altitude has led to it being called the Highest State, and it has even been called the Buffalo Plains State because of the bison that once roamed there.

The Territory of Colorado was created by the U.S. Congress in 1861. Its name came from the Rio Colorado — the Colorado River — which was named by Spanish explorers in the region. In Spanish, colorado means "colored red."

Sixteen years later, on 1 August 1876, the State of Colorado was admitted to the Union and became the 38th state. That year, the U.S. was celebrating the 100th anniversary of the signing of the Declaration of Independence. Among the events held that year was the Centennial Exposition, which was held in Philadelphia, Pennsylvania, and was the first World's Fair to be held in the U.S. As the only state admitted that year — the only one between 1867 and 1889, in fact — Colorado became known as the Centennial State.

Colorado's would not be called the Centennial State if it had been accepted as a state on its first try. The U.S. Congress passed an act that would have allowed Colorado to be granted statehood in 1865 — 11 years before the United States' centennial — but then-president Andrew Johnson vetoed the act. Johnson was succeeded by Ulysses S. Grant in 1869, and in 1870, Grant began advocating for Colorado to be admitted as a state. On 3 March 1875, the U.S. Congress again authorized Colorado to become a state, and Grant signed Proclamation 230 - Admission of Colorado Into the Union in 1876.