The state of Maryland is served in two geographically distinct numbering plan areas in the North American Numbering Plan (NANP), which are each served with three overlay area codes.
Areacode Yearcreated ParentNPA Overlay Numbering plan area 301 1947 – 227/240/301 Western Maryland, including its suburbs of Washington, D.C. 240 1997 301 227 2023 240/301 410 1991 301 410/443/667 Eastern Maryland including Baltimore and Annapolis 443 1997 410 667 2012 410/443