Aurora is a Home Rule Municipality spanning Arapahoe, Adams, and Douglas counties in Colorado. The city is the third most populous city in the state of Colorado and the 58st most populous city in the United States. The city had an estimated population of 319,057 in 2008-07-01. The city and its western neighbor are the principal cities of the Denver-Aurora-Broomfield, CO Metropolitan Statistical Area, which in 2007 had an estimated population of 2,464,866. (22nd most populous MSA), the estimated population of the Denver-Aurora-Boulder Combined Statistical Area was 2,998,878 on 2007-07-01 (15th most populous CSA).