Indianapolis colloquially known as Indy, is the state capital and most-populous city of the U.S. state of Indiana and the seat of Marion County. According to the United States Census Bureau, the consolidated population of Indianapolis and Marion County in 2020 was 977,642. The "balance" population, which excludes semi-autonomous municipalities in Marion County, was 887,642. It is the 15th most populous city in the U.S., the third-most populous city in the Midwest, after Chicago, Illinois 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 2,048,703 residents. Its combined statistical area ranks 28th, with a population of 2,431,361. Indianapolis covers 368 square miles (950 km2), making it the 16th 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 Delaware 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 1-square-mile (2.6 km2) 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 reflect its historical ties to transportation—the "Crossroads of America" and "Railroad City". 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 29th largest economic region in the U.S., based primarily on the sectors of finance and insurance, manufacturing, professional and business services, education and health care, government, and wholesale trade. 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 clubs, four university campuses, and several museums, including the world's largest children's museum. However, the city is perhaps best known for annually hosting the world's largest single-day sporting event, the Indianapolis 500. Among the city's historic sites and districts, Indianapolis is home to the largest collection of monuments dedicated to veterans and war casualties in the U.S. outside of Washington, D.C.
Economic development initiatives focused on revitalizing the city's downtown continued in the 1990s under the mayoral administration of Stephen Goldsmith. During this period, a number of cultural amenities were completed at White River State Park, the Canal Walk continued development, Circle Centre Mall was completed, and new sports venues (Victory Field and Conseco Fieldhouse, now Gainbridge Fieldhouse) were opened. In 1999, several cultural districts were designated to capitalize on cultural assets within historically significant neighborhoods unique to the city's heritage as a means to promote continued economic development.
During the 2000s, the city invested heavily in infrastructure projects, including two of the largest building projects in the city's history: the $1.1 billion Indianapolis International Airport Colonel H. Weir Cook Terminal and $720 million Lucas Oil Stadium, both opened in 2008. A $275 million expansion of the Indiana Convention Center was completed in 2011. Construction began that year on DigIndy, a $1.9 billion project to correct the city's combined sewer overflows by 2025. Rapid transit was reintroduced to Indianapolis with the opening of IndyGo's $96 million Red Line bus rapid transit project in 2019.
Indianapolis is in the East North Central region of the Midwestern United States, in central Indiana. According to the U.S. Census Bureau, the Indianapolis (balance) encompasses a total area of 368.2 square miles (954 km2), of which 361.5 square miles (936 km2) is land and 6.7 square miles (17 km2) is water. The consolidated city boundaries are coterminous with Marion County, with the exception of the autonomous municipalities of Beech Grove, Lawrence, Southport, and Speedway. Indianapolis is the 16th largest city by land area in the U.S.
Indianapolis is within the Tipton Till Plain, a flat to gently sloping terrain underlain by glacial deposits known as till. The lowest point in the city is about 650 feet (198 m) above mean sea level, with the highest natural elevation at about 900 feet (274 m) above sea level. Few hills or short ridges, known as kames, rise about 100 feet (30 m) to 130 feet (40 m) above the surrounding terrain. The city lies just north of the Indiana Uplands, a region characterized by rolling hills and high limestone content. The city is also within the EPA's Eastern Corn Belt Plains ecoregion, an area of the U.S. known for its fertile agricultural land.
Topographic relief slopes gently toward the White River and its two primary tributaries, Fall and Eagle creeks. In total, there are about 35 streams in the city, including Indian Creek and Pogue's Run. Major bodies of water include Indian Lake, Geist Reservoir, and Eagle Creek Reservoir.