1990. Split Despite the overall growth of the Baltimore–Washington metropolitan area, 301 remained the exclusive area code for Maryland for 44 years, making Maryland one of the largest states with a single area code. By the end of the 1980s, however, it became apparent that breaking seven-digit dialing in the Washington area would not free up enough numbers north of the Potomac River to stave off the immediate need for a new area code. Baltimore and the Eastern Shore were split off as area code 410 on November 1, 1991. The split largely followed metropolitan area lines. There were a few exceptions, such as in Howard County, which is often recognized as part of the Baltimore metropolitan area, a small portion of the county remained in area 301, while the rest of the county was reassigned to area code 410. When an area code is split, the largest city, in this case Baltimore, in the old numbering plan area typically retains the existing area code to minimize expense for changing telephone numbers. in this case, however, Bell Atlantic spared the large number of federal agencies on the Maryland side of metropolitan Washington from the expense and disruption. First overlay Although the area code split was intended as a long-term solution, within four years 301 was close to exhaustion due to the proliferation of cell phones and pagers, especially in the Washington suburbs. In relief action, area code 240 was introduced on June 1, 1997, to form the state's first overlay. Overlays were a new concept at the time, and met with some resistance due to the requirement for ten-digit dialing. It was decided to create an overlay rather than split the region into two new regions in order to avoid assigning a new area code to 1.2million existing phone numbers. At the time, it was predicted that it would take until 2008 to exhaust area code 240. Second overlay A September 2022 study projected that the 301/240 numbering plan area would suffer central office code exhausted between April and June 2023. The North American Numbering Plan Administrator has assigned area code 227 as an additional overlay code for the region. Assignment of telephone numbers with area code 227 begins on June 14, 2023. Service area The numbering plan area 301/240 include the counties of Allegany, Charles, Garrett, Montgomery, Prince George's, St. Mary's and Washington counties, most of Frederick County, western