area codes were introduced in 1947, all numbers followed the pattern N0X or N1X (where the middle digit was either a zero or one). By 1994, area code 610 was the last remaining code in this group. The next new area codes to be assigned (334 in Alabama and 360 in Washington, both in 1995) were the first to break this rule. Service area Counties The numbering plan area for Pennsylvania by count is: Berks County - All but extreme western portions (in 717), extreme northern portions (in 570) and Hereford area (served by the Pennsburg exchange in the 215/267 area code). Bucks County - Northeastern portion served by the Coopersburg, Springtown, Riegelsville and Ferndale exchanges. Chester County - All but the extreme western portion [which is served by the (717-442) Gap exchange]. Delaware County - All Lancaster County - Far southeastern portion of the county only, centered on the town of Christiana. Rest of county uses the 717 area code. Lebanon County - Newmanstown is the only Lebanon County municipality to use 610 as its area code, specifically 610-589-XXXX (also shared with Womelsdorf, Berks County). Lehigh County - All but extreme southwestern portion, served by the Pennsburg exchange in the 215/267 overlay. Montgomery County - Southern and western portions; other areas are served by the 215/267 area codes. New Castle County, Delaware - A few houses along West Ridge Road and Sterling Avenue in Lower Chichester, Pennsylvania/Claymont, Delaware straddle the border but have Pennsylvania phone numbers. Northampton County - All but extreme northeastern portions, such as Portland and Upper Mount Bethel Township, which are in the 570 area code Carbon County - Southern portion, served by the 377 Lehighton and the 824 and 826 Palmerton exchanges. The western end of the county, including Lansford and Summit Hill, may use 610/484 for mobile and digital numbers while retaining 570-645 for conventional phone numbers. Monroe County - Far southwestern portion Schuylkill County - The southern and eastern fringes of this county, including portions of East Brunswick, West Brunswick, and West Penn Township (served by the Lehighton, Germansville, and Kempton exchanges) and Port Clinton borough are assigned 610/484, however the majority of it is in 570/272, and even smaller portions (including Tower City) are in 717. Towns and cities The following towns and cities are included in the numbering plan area: Allentown, Bethlehem, Catasauqua, Chadds Ford, Chester, Christiana, Downingtown, Easton, Emmaus, Exton,