Florida

Florida is the 27th state in the United States of America. It has been referenced multiple times throughout the franchise:
 * In Postcards From Buster, Buster visits Miami, Florida in "Home Sweet Home" and Cocoa Beach, Florida in "Riding the Wave."
 * In the book Arthur's Classroom Fib, it is mentioned that over the summer, Binky visited Disney World, which is in Orlando, Florida.
 * Also in Arthur's Classroom Fib, it is mentioned that one of the places Buster went with his dad was Florida, where he saw alligators.