The Mile High Illinois, Illinois Sky-City, or simply The Illinois was a proposed skyscraper that would have been 1 mile (1,600 m) high, envisioned by Frank Lloyd Wright in 1956. The design, intended to be built in Chicago, would have included 528 stories, with a gross area of 18,460,000 square feet (1,715,000 m2). Had it been built, it would have been the tallest building in the world by far, being more than four times the height of the then tallest building in the world, the Empire State Building, and it would be nearly twice as tall as the world's current tallest building, the Burj Khalifa.

The building is one of the semi-serious visionary buildings meant to be an alternative to the increasing urban sprawl occurring in most cities. None of these has ever been viewed as financially feasible.

The design of the Burj Khalifa, the current tallest building in the world, is said to have been inspired by that of The Illinois

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