It'd be interesting to see some research on that. Most of the plants I'm aware of aren't actually in Detroit proper, but the metro area.
A quick glance over the list of GM factories[1] shows just one assembly plant in the city. Chrysler has a bit more going on[2] in Detroit. Of course, this doesn't take into account all of the suppliers, which is a huge omission. In my experience growing up in the area, it wasn't so uncommon for someone to be working for a company whose sole customer was one of the Big Three.
It's not just the big three auto plants. There is all of the ancillary plants that make the parts and sub-assemblies. Raw materials, Logistics, Accounting, Foodservice, and everything else that goes along with productive activity.
A quick glance over the list of GM factories[1] shows just one assembly plant in the city. Chrysler has a bit more going on[2] in Detroit. Of course, this doesn't take into account all of the suppliers, which is a huge omission. In my experience growing up in the area, it wasn't so uncommon for someone to be working for a company whose sole customer was one of the Big Three.
[1]: http://en.wikipedia.org/wiki/List_of_General_Motors_factorie...
[2]: http://en.wikipedia.org/wiki/List_of_Chrysler_factories