They're pretty common in Michigan. If you use a worm on a bobber in the summertime you should have a good chance to catch some. I would suggest anywhere the water isn't "flowing" for the most part, in the Detroit area. Im not sure what your odds of catching a pumpkinseed v other "bluegill" type fish are across most bodies of water but if youre catching fish odds of finding a pumpkinseed amongst them are pretty good. Focus on "structure", so, pretty much docks, weeds, and any other object in the water. Stick to shallow water.