Bumped into a traveler a little while ago who showed me what he said was a fragment of the actual Liberty Bell! Poppycock! The Liberty Bell is still intact and laying in the ruins of Philly. I have funded an expedition to that dump in hopes of having the entire bell brought back to my museum.”— Liberty Bell Expedition, Abraham Washington
The city of Philadelphia (colloquially called Philly) lies in ruins, but one piece of American history still stands there, the Liberty Bell. Philly is mentioned in Abraham Washington's terminal. It states that he ran into a traveler from there, and that he has funded an expedition to retrieve the Liberty Bell.
Philadelphia is mentioned only in Fallout 3.