Centennial is a Home Rule Municipality located in Arapahoe County, Colorado, United States. The city population was 100,377 at the 2010 United States Census. Centennial is a part of the Denver-Aurora-Lakewood, CO Metropolitan Statistical Area. Centennial is the tenth most populous municipality in the state of Colorado and its 2001 city incorporation was the largest in U.S. history. Centennial is ranked as the 15th-safest city in the country.
The City of Centennial was formed on February 7, 2001, from portions of unincorporated Arapahoe County, including the former Castlewood and Southglenn census-designated places (CDPs). The citizens of the area had voted to incorporate on September 12, 2000, choosing Centennial as the official name during the vote. The name reflects Colorado's admission to the Union as the 38th state in 1876, the centennial year of the United States Declaration of Independence. The state of Colorado is nicknamed the "Centennial State".
Incorporation was approved by 77% of the voters, and the population of the area at over 100,000 made it the largest incorporation in U.S. history as of its creation. The city was incorporated in large part to prevent further annexations of unincorporated areas by the city of Greenwood Village in an attempt to improve its tax base.