The city of Centennial is a Home Rule City located in Arapahoe County, Colorado, United States, and part of the Denver-Aurora metropolitan area. The city was to have a total population of 100,377 in 2010 census. Centennial is the tenth-most populous municipality in the state of Colorado and its 2001 incorporation was the largest in U.S. history. Centennial is ranked as the 15th safest city in the country.
Centennial was formed 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. 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 by the city of Greenwood Village in the I-25 corridor to improve its tax base. The taxes generated from businesses in the unincorporated portions of Arapahoe County funded the majority of the county's services, including road work. There were a number of court cases establishing the right of incorporation to take precedence over the right of annexation.
The city was incorporated on a promise to keep city taxes at 1% (one of the campaigns against incorporation appealed to maintain the 3.8% sales tax of the unincorporated county). According to the City of Centennial website, the current sales tax rate is two and one-half times this rate, at 2.5%.