I would suspect the Midwest is sort of in between California and New York. There's a strong social pressure to dress up for dressy events, but no one's going to press a jacket upon you, or refuse you entry if you're dressed inappropriately.

On a side note, I should really see about taking that lovely silk Marc Jacobs skirt you bought me in to the tailor. I just hope they can actually alter it - I'm a little worried that the construction of it will make that unlikely.