The state of Indiana began selling off plots of land to railroads and speculators after 1851 to fund the local school system.

[9] The 1900 census gives a total population of just 3,411, but the arrival of Inland Steel in 1903 transformed the city into an industrial powerhouse.

Inland Steel dominated the city's economy through the 1990s, and expanded its massive integrated mill at Indiana Harbor multiple times through the 1980s.

[10] By 1907, East Chicago boasted a navigable waterway link to Lake Michigan and to the Grand Calumet River: the Indiana Harbor Ship Canal.

Steel mills, petroleum refineries, construction firms, and chemical factories operated at Indiana Harbor and along its inner canal system.

Locals spoke of the “Twin City” to describe spatial, residential, and class divisions at the heart of the town's identity.

The small Mexican community was targeted for voluntary and forced repatriation during the 1930s and 1950s (1,800 were deported in 1932 alone), but those who remained eventually paved the way for later Latino immigration after 1965.

Black Americans also began to arrive in the 1910s and 1920s as part of the first wave of the Great Migration, and this continued from the 1940s to 1960s.

There were also a large number of families that identified as Puerto Rican, Romanian, Serbian, Italian, Lithuanian, and Croatian.

Over 70 nationalities were represented, with over 59 congregations of the Protestants, Orthodox, Catholic Churches, as well as Jewish synagogues.

Like neighboring Gary, Indiana, East Chicago quickly developed a reputation as a rough industrial city, plagued by extreme pollution, ethnic and racial tensions, organized crime, illegal gambling and clubs, political corruption, prostitution, and other vices.

However, East Chicago's population began to decline in the 1960s as suburbanization, white flight, affordability of automobiles, and the construction of highways meant that workers no longer had to live in the city, but could commute from less-polluted suburbs.

[20] Residents' decades-long concerns about lead contamination were confirmed in 2016 via EPA testing, especially affecting over 270 families in the West Calumet Housing Complex.

[21][22] As governor of Indiana, Mike Pence declined to declare the Superfund site a state emergency;[23] his successor Governor Eric Holcomb has issued Executive Order 17-13, declaring a disaster emergency in East Chicago.

US 12 and US 20 go through the Indiana Harbor and East Chicago sections of the city, respectively, before joining up on both sides.

PACE operates Route 892, a special work shuttle between Gary, East Chicago and UPS' Hodgkins facility.

Other large employers include Amoco Oil Co., Union Tank Car, American Steel Foundries, USG Corp. and St. Catherine Hospital.