1776

The Freedom Tower, officially names 1 World Trade Center, is officially the tallest building in the US.  The spire reaches 1776 feet (541 meters) which is symbolic because the Declaration of Independence was signed in the year 1776 CE.

If you don't include the antenna, the height is only 1368 feet (417 meters).

The Sears Tower, which had been the tallest building in the United Sates is 1450 feet.

The World Trade Center (of blessed memory) had been 1368 feet.

The Burj Khalifa, in Dubai, is the tallest building in the world.  It is 2717 feet.