Great Lakes Region:
Illinois, Indiana, Minnesota, Michigan, North Dakota, Ohio, South Dakota, Wisconsin
Southwest Region:
Arkansas, Louisiana, New Mexico, Oklahoma, Texas
Eastern Region:
New Jersey, New York, Pennsylvania, Virginia, and West Virginia
Here is the link:
Regional Flight Surgeon Contact Information
I've heard it's not always processed in the same region that you have your medical appointment completed in. With that said, that is from just reading on the forums, I have nothing to back that up.
I did my medical in the Great Lakes Region and I was cleared in the Great Lakes Region 3 months after my medical appointment.