They did film Gran Torino in detroit.
Yep.
In one of the shittiest areas possible, Highland Park.
Out there on the interweb, somewhere, is a great photo-essay done on Highland Park.
The photographer travelled through out that dilapidated and abandoned shithole, taking some incredibly revealing photos.
One series was filmed in the Highland Park police headquarters, which looked as if the police had abandoned it in the middle of the night. Old mug shots, criminal records and even gun parts scattered throught the station.
Originally, Gran Torino was set in Wisconsin or Minnesota (?), but they thought a Detroit scenario would be more relevant to the audience.