Independence Hall is the Philadelphia building most closely associated with the Declaration of Independence.
The Second Continental Congress met in the building, then known as the Pennsylvania State House, and adopted the Declaration in 1776. The Constitutional Convention also met there in 1787 and produced the United States Constitution.
The building’s dual connection to independence and constitutional government makes it central to America250 history. Its Assembly Room contains the chair used by George Washington when he presided over the Constitutional Convention.
Federal Hall in New York City is important because Congress met there under the Articles of Confederation and Washington took the presidential oath there. Faneuil Hall and Carpenters’ Hall are also significant colonial-era sites, but neither is the canonical answer here.