As I'm sure you know, Minneapolis is a huge advertising town. I'm probably not the best person to ask about working as a freelance advertising/marketing designer in Minneapolis, though, as that's not what I do.

What I can say as someone who used to freelance while living in Minneapolis is that the vast majority of my clients were remote and I had only a handful of local clients. In my experience, being a successful freelancer is much more about forging positive connections with clients and peers through your work more than living in close proximity to one's clients.

Do good work and more work will come.