The City of 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 incorporation was the largest in U.S. history. Centennial is ranked as the 15th safest city in the country.entennial 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.