Old St. Mary's Catholic Church, built in 1763, was the site of the first public religious celebration of the Declaration of Independence. Members of the Continental Congress officially attended services and George Washington worshiped here on at least two occasions. So too did John Adams and George Mason, neither of whom were known for their affection toward Catholicism. In fact, the entire Virginia delegation—"except the General"—attended Mass here prior to the opening of the Convention. Having expressed a sympathetic reception to the early parts of the service, Mason gets a bit irritated: "While I was pleased with the Air of Solemnity so generally diffused thro' the Church, I was somewhat disgusted with the frequent Tinkling of a little Bell; which put me in Mind of the drawing up the Curtain for a Puppet-Shew. I wonder they have not substituted some more solemn & deep-toned instrument."

Thomas Fitzsimons and Commodore John Barry are buried here.

Barry, an Irish immigrant, has a statue erected in his honor on the south side of Independence Hall. Why it is there is a mystery and the conventional response is that it is to honor the "Father of the American Navy," as he has come to be known. But there is another explanation that at least makes for a good Irish story. Word has it that Barry led a group of pro-constitutionalists, in late September 1787, and hauled Antifederalists from taverns and churches. He brought them to Independence Hall so that the Pennsylvania Assembly could secure the quorum needed to pass a resolution endorsing the Pennsylvania Ratifying Convention. What better way than to honor Barry with a statue at Independence Hall!

According to Billy Smith, between 1789-1793, 53% of all immigrants to Philadelphia came from Ireland and 27% came from France and the French West Indies because of political turbulence. This amounts to an influx of roughly 2,000 Catholics a year into Philadelphia during this five year period.