Indianapolis (ˌɪndiəˈnæpəlᵻs ), colloquially known as Indy, is the capital and most populous city of the U.S. state of Indiana and the seat of Marion County. According to the 2020 United States census, the balance population was 887,642. It is the 16th-most populous city in the U.S., the third-most populous city in the Midwest after Chicago and Columbus, Ohio, and the fourth-most populous state capital after Phoenix, Arizona, Austin, Texas, and Columbus. The Indianapolis metropolitan area is the 33rd-most populous metropolitan statistical area in the U.S., with 2,111,040 residents. Its combined statistical area ranks 28th, with a population of 2,431,361. Indianapolis covers , making it the 18th largest city by land area in the U.S.
Indigenous peoples inhabited the area dating to as early as 10,000 BC. In 1818, the Lenape relinquished their tribal lands in the Treaty of St. Mary's. In 1821, Indianapolis was founded as a planned city for the new seat of Indiana's state government. The city was platted by Alexander Ralston and Elias Pym Fordham on a grid next to the White River. Completion of the National and Michigan roads and arrival of rail later solidified the city's position as a manufacturing and transportation hub. Two of the city's nicknames, the "Crossroads of America" and "Railroad City", reflect the city's historical ties to transportation. Since the 1970 city-county consolidation, known as Unigov, local government administration operates under the direction of an elected 25-member city-county council headed by the mayor.
Indianapolis anchors the 30th-largest economic region in the U.S., based primarily on the industries of trade, transportation, and utilities; professional and business services; education and health services; government; leisure and hospitality; and manufacturing. The city has notable niche markets in amateur sports and auto racing. The city is home to three Fortune 500 companies, two major league sports teams, the Indianapolis Colts of the National Football League and the Indiana Pacers of the National Basketball Association, five university campuses, and several museums, including the world's largest children's museum.