city, Adams, Arapahoe, and Douglas counties, north-central Colorado, U.S. An eastern suburb of Denver, Aurora was the third most populous city in Colorado at the start of the 21st century and, occupying 280 square miles (725 square km), the state's largest city in area. Founded during the silver boom of 1891 and named Fletcher after its Canadian-born founder, Donald Fletcher, it flourished as a mining centre until 1893, when a silver panic closed the mines. In 1902 Adams county was created from Arapahoe county, and the division line split the community, placing it in two counties; a portion of the present city also falls within Douglas county. Fletcher was renamed Aurora in 1907. The city is mainly residential but has some light manufactures (including fishing tackle and sporting goods, electronic equipment, luggage, and precision metal products). It also is the site of Buckley Air National Guard Base. In 1996 the Fitzsimons Army Medical Center was closed, and the area became the site of an immense redevelopment project. The decommissioned base was turned into a health and research park, featuring a branch campus of the University of Colorado. Denver International Airport lies to the northeast. Inc. 1891. Pop. (1990) 222,103; (2000) 276,393.

city, Kane and DuPage counties, northeastern Illinois, U.S. It lies on the Fox River, about 40 miles (65 km) west of Chicago. Founded in 1834 by settlers from New York, it was originally known as McCarty's Mills. A trading point and mill site near a Potawatomi Indian village, the town was laid out in 1836 and renamed Aurora in 1837. It developed as both a residential and an industrial city largely because of its key position along the Chicago, Burlington and Quincy Railroad. In 1881 Aurora became the first city in Illinois to install electric streetlights.

The city's manufactures include heavy machinery, industrial and electrical equipment, woven cotton fabrics, timing products, rod end and spherical bearings, masonry accessories, and furniture. Casino gambling and the insurance industry also contribute to the economy. Aurora University (originally Mendota Seminary), founded in 1893 at Mendota by the Advent Christian Church, relocated to Aurora in 1912; its campus includes a centre for Native American culture. Waubonsee Community College, named for a local Potawatomi chief, was established in 1966 in Sugar Grove, a few miles west. The Aurora Historical Society museum, sited in a home built in 1857, includes locally excavated mastodon bones. Blackberry Farm's Pioneer Village features an 1840s farm. The Fermi National Accelerator Laboratory, a physics research facility containing the world's most powerful particle accelerator, is in Batavia, just north of the city. Inc. 1857. Pop. (1990) 99,581; (2000) 142,990.