I may need a little more clarification, but I'll take an initial stab and if I'm way off, please redirect me.

You can use Location Type to group locations in Locator. If you set all locations to Michigan and set Locator to only display the type "Michigan" this would restrict your instance of Locator to only Michigan.

I'm guessing this isn't exactly what you're looking for because it sounds like the locations are only in Michigan. If you're using state as a search restriction and you'd like to default state to Michigan, I'm afraid the answer is no. Locator uses the DNN list for region. Without modification to the code, Locator uses the standard list.

Since Locator is using the standard list of regions I don't think you'd want to strip down the regions list to just Michigan. Locator currently doesn't have a default region so we don't have the ability to default a state in the list.