The 78 is an undeveloped plot of land in South Loop, Chicago stretching from Roosevelt Road south to 16th Street, and Clark Street west to the Chicago River. Its name refers to the existing 77 community areas in Chicago.

It was the site of an unrealized 2018 megadevelopment proposal for several office and residential towers, high-rises, and a riverwalk. Since 2016 Related Midwest is the owner of the site. Although the Chicago City Council approved the megadevelopment in April 2019 (including a tax increment financing agreement), it was not built. The megadevelopment was to include a $1.2 billion research center called the Discovery Partners Institute, which would have been operated by the University of Illinois.

In 2021, it was proposed to put a Rivers Casino in The 78 as part of the Chicago Casino Proposals, but the city selected a site in the River West district near the intersection of Chicago Avenue and Halsted Street.

In June 2025, the owner of the Chicago Fire FC soccer team proposed to build a soccer stadium on the site.

The mixed use development notion of 2018 in The 78 was to be located on a 62-acre parcel of land just south of Downtown Chicago and north of Chinatown. The area is bordered by Roosevelt Road to the north, Clark Street to the east, 16th Street to the south, and the South Branch of the Chicago River to the west.

Much of the land was created through landfills in the 1920s as part of a $9 million realignment of the South Branch of the Chicago River. The area then became a railyard for trains traveling to or from either the Grand Central station or LaSalle Street station.

The railyard was eventually demolished in the 1970s, forming a 62-acre vacant lot. The former railyard remained in limbo for decades. In 2001, Tony Rezko bought the entire land for mixed-use development. His plan did not come to fruition and he eventually sold the land in 2005.

Many plans have been proposed or discussed for this site. Related Midwest acquired the land in 2016.