Though I'm not familiar with EVERY city you listed I feel Minneapolis is the best place to raise kids (over Concinatti, Detroit, or St. Louis). I didn't list Chicago because it is so large (there are very nice and very bad places there, so it's really a matter of location).
I live in Eagan (a St. Paul suburb) and have no trouble finding a group of at least 7-8 triathletes to workout out with every single day. If I had to pick I would suggest checking out southern and western suburbs (e.g., Edina, Minnetonka, Apple Valley, Eagan, St. Louis Park, Eden Prairie...). It really depends on what type of neighborhood you are looking for and where you plan on sending your kid(s) to school.
In MN most any local public school will get the job done. Though I've noticed better public education on the east coast (I'm not familiar with the west side) schools here are safe and well funded. As for private schools, there are a few in St. Louis Park (i.e., Benilde St. Margaret's, Breck, Blake) and another couple in Mendota Heights (i.e., St. Thomas Academy, The Convent of the Visitation) which is closer to where I live.
It's a great place to raise kids and train for tris. Feel free to shoot me over a message or give me call to learn more.
Tri Sites Based in Mpls/St. Paul
http://www.Triathlete.com http://www.MidwestEvents.com http://www.MnTriClub.com Another FYI: stud triathletes in the area include David Thompson (honerable mention for USAT Triathlete of the Year), Tony Schiller (also honerable mention, former winner of triathlete and master of the year... If I remember correctly), Jan Guenther (another former master's winner)... Oh yeah... I almost forgot... the fastest and most studly of them all (Giancarlo Canessa)... that's me ;-)
Though I'm not familiar with Indy, my brother is, I can get some more info from him. If you want any more info, let me know.
-gc