231 is a North American telephone area code in the U.S. state of Michigan. Area Code 231 includes the Northwestern part of Michigan's Lower peninsula. Areas included are Muskegon, Petoskey, Ludington, Baldwin, Traverse City, and Pentwater. It was created in June 1999 as a split from area code 616. 231 is essentially the northern half of the old 616 area code. 616 previously covered the entire western half of the state of Michigan, extending west from the north-south line aligned with the Mackinac Bridge.