Aurora (, ) is a Home Rule Municipality in the U.S. state of Colorado, spanning Arapahoe and Adams counties, with the extreme southeastern portion of the city extending into Douglas County. Aurora is one of the principal cities of the Denver-Aurora-Lakewood, CO Metropolitan Statistical Area. The city's population was 325,078 in the 2010 census, which made it the third most populous city in the state of Colorado and the 54th most populous city in the United States.
The Denver-Aurora-Lakewood, CO Metropolitan Statistical Area had an estimated population of 2,645,209 on July 1, 2012 (the 19th most populous MSA in the U.S.) Denver and Aurora combined make up less than half of the metro area's population and Aurora has approximately half the population of Denver. The estimated population of the Denver-Aurora, CO Combined Statistical Area was 3,214,218 on July 1, 2012 (15th most populous CSA).
Before European settlement, the land that now makes up Aurora was the territory of the Arapaho, Cheyenne, Núu-agha-tʉvʉ-pʉ̱ (Ute), and Očeti Šakówiŋ (Sioux) tribes. Aurora originated in the 1880s as the town of Fletcher, taking its name from Denver businessman Donald Fletcher who saw it as a real estate opportunity. He and his partners staked out four square miles (10 km2) east of Denver, but the town - and Colorado - struggled mightily after the Silver Crash of 1893. At that point Fletcher skipped town, leaving the community with a huge water debt. Inhabitants decided to rename the town Aurora in 1907, after one of the subdivisions composing the town, and Aurora slowly began to grow in Denver's shadow becoming the fastest-growing city in the United States during the late 1970s and early 1980s. Aurora, composed of hundreds of subdivisions, thus carries the name of one of the original development plats from which it sprang.