Depends on what you enjoy growing. Often the busiest (and most helpful) forums are not regional/state-specific, but deal with various types of gardening. Perennials and Trees have been excellent forums in my experience.

For me, I enjoy many different types of plants, a bit of a snob about geraniums, not pelargoniums. But I am interested in regional forum or group that I can learn about what does best for the area, but I don't think there is such a one for the area I moved to. The Georgia Gardener was special in that we met and swapped plants, some of which have become the best and most loved pass along plants, but especially met some great people, too!

Try the Midwest Gardening forum.