Lots of them. “Ghost towns” is an exaggeration. But Detroit has shrunk from 1.8 million to 650,000 and that’s caused tremendous economic problems. Philadelphia has shrunk from over 2 million to about 1.5 million and is stuck in a constant state of stagnation. Chicago has shrunk from 3.6 million to 2.6 million. It’s in much better shape than the other two, but went from being the “Second City” to a one with a questionable future. Baltimore shrank from nearly a million people to under 600,000, and seems to be in a state of terminal decline. Pittsburgh almost hit 700,000, and now is less than half that. The city has enjoyed a recent resurgence due to CMU and biotech, but the prosperity is not widely shared, and the city is kind of a museum to its more prosperous heyday.