24, 2012. This had the effect of assigning 24 million numbers to just over four million people. Based on current projections, a fourth area code will not be required in the region until about 2030. Coverage The counties served by these area codes include: In the Baltimore metropolitan area: All of Baltimore City and Baltimore, Calvert and Harford counties Most of Anne Arundel, Carroll and Howard counties A small portion of eastern Frederick County All of Maryland's Eastern Shore: Caroline County Cecil County Dorchester County Kent County Queen Anne's County Somerset County Talbot County Wicomico County Worcester County Explanatory notes References External links List of cities covered and exchanges from Area-Codes.com, 410 Area Code List of cities covered and exchanges from Area-Codes.com, 443 Area Code 410 410 Communications in Baltimore Telecommunications-related introductions in 1991 Telecommunications-related introductions in 1997 Telecommunications-related introductions in 2012