<imagemap> image:Area code 301.svg|right|300px|thumb|alt=area codes 227, 240, and 301. These numbers are related to the main zip codes of Maryland.|Maryland consists of the red and blue areas. The red area has area codes 227, 240 and 301. poly 336 37 323 30 310 13 305 -2 337 2 Area codes 215, 267, and 445 poly 339 121 325 118 296 86 296 73 307 56 319 51 328 48 327 42 337 34 Area code 856 poly 248 1 257 11 265 35 253 43 264 50 258 64 278 67 286 56 294 54 305 58 328 47 324 41 335 35 322 30 304 -2 Area code 484 poly 85 65 88 53 101 43 109 48 111 33 100 12 94 4 100 -1 245 -1 258 12 266 35 250 43 263 50 256 66 Area code 717 poly 36 1 43 9 38 19 37 29 17 44 14 67 84 66 87 53 101 44 106 48 111 35 96 5 96 -1 Area code 814 poly 2 2 0 65 16 68 18 43 39 30 40 17 45 10 35 2 Area code 724 poly 181 143 184 134 195 144 186 156 184 147 182 142 Area code 202 poly 168 182 169 171 177 170 176 165 184 162 184 152 179 139 168 135 171 131 148 123 141 129 148 166 Area code 571 poly 327 230 290 235 282 236 283 246 317 243 Area codes 757 and 948 poly 336 153 335 186 288 188 277 69 286 56 294 55 303 57 298 76 299 88 316 129 Area code 302 poly 337 190 327 226 278 242 235 193 219 187 214 168 211 157 211 135 205 121 201 116 198 109 200 105 173 94 175 86 167 66 275 67 288 188 Area codes 410, 443, and 667 poly 0 68 -1 184 16 191 22 186 38 151 51 159 85 118 88 103 87 90 125 121 133 106 135 97 129 92 128 87 122 84 126 81 126 75 116 77 104 68 98 69 93 75 86 73 81 77 79 84 69 84 61 81 59 76 59 73 54 74 43 93 37 88 32 87 31 94 4 117 5 67 Area code 304/681 poly 247 250 249 239 221 220 214 212 200 213 189 199 184 211 169 211 142 226 121 223 106 243 113 248 Area code 804 poly 48 250 34 235 60 212 84 208 79 192 77 189 93 172 106 185 122 223 106 243 107 247 Area code 434
poly 1 248 1 184 15 193 22 187 39 151 49 159 58 142 62 147 67 137 69 140 84 118 88 102 87 90 126 123 135 105 138 107 144 105 149 110 153 112 154 114 147 120 149 123 142 131 148 168 167 182 164 189 169 199 179 199 185 193 189 198 183 211 168 211 143 227 121 224 106 184 94 172 78 189 85 208 61 211 34 237 44 247 Area code 540
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Area codes 301, 240, and 227 are telephone area codes in the North American Numbering Plan (NANP) for the western part of the U.S. state of Maryland. The numbering plan area (NPA) comprises Maryland's portion of the Greater Washington, D.C. metro area, portions of southern Maryland, along with rural western Maryland. This includes the communities of Cumberland, Frederick, Hagerstown, Gaithersburg, Potomac, Germantown, Bethesda, Rockville, Landover, Silver Spring, and Waldorf.
Area code 301 was the first area code for all of Maryland, from 1947, when the area code system was created, until 1991, when everything from Baltimore eastward was split off as area code 410. In 1997, area code 240 was added as an overlay area code for the 301 territory. On June 14, 2023, a third overlay code, 227, was added to provide more central office prefixes for new telephone numbers.
Area code 301 was one of the original North American area codes when the American Telephone and Telegraph Company (AT&T) established a new, nationwide telephone numbering plan in 1947. The area code served the entire state of Maryland.
Much of the Washington metropolitan area is part of a local calling area which is centered on the District's area code 202, and also extends into the suburban area in southern Maryland with 301 and Northern Virginia with area code 703. From 1947 to 1990, it was possible to dial any other telephone number in the metro area as a local call with only seven digits, not using an area code, irrespective of the home area code. The entire metro area was also reachable via long-distance services by dialing area code 202, for which purpose AT&T had established cross-referenced operator routing codes for all affected central offices. This was implemented via a system of central office code protection, meaning that no central office code in the metro area could exist in more than a single central office. For example, if 202-574 numbers were in use in the District or 703-574 numbers were in use in Northern Virginia, the corresponding 301-574 numbering block could only be assigned in areas considered a safe distance away from the capital, such as the Eastern Shore of Maryland.
By the end of the 1980s, the Washington metropolitan area was running out of assignable prefixes for new central offices on both sides of the Potomac River. The only unassigned prefixes were unavailable due to the central office code protection that maintained seven-digit dialing in the metro-area. Assignment of these prefixes would require dialing an area code. The three local operating companies of the Chesapeake and Potomac Telephone Company (C&P Telephone, later part of Bell Atlantic and now Verizon) cooperated in ending code protection for the Washington area on October 1, 1990. Ten-digit dialing was now required for all local calls between Maryland, the District of Columbia, and Virginia. Area code 202 was no longer usable for suburban points. Local calls within Maryland did not require the area code. Permissive dialing using the old dialing procedures continued from April 1 through October 1, 1990.
Due to the overall growth of the BaltimoreâÂÂWashington metropolitan area, it became apparent by the end of the 1980s that terminating central office code protection in the Washington area could not free up sufficient resources north of the Potomac River to stave off the immediate need for a new area code.
In mitigation action, Baltimore and the Eastern Shore were split off as a new numbering plan area with area code 410 on November 1, 1991. The area code split largely followed metropolitan area lines with a few exceptions. While Howard County is often recognized as part of the Baltimore metropolitan area, a small portion of the county remained in 301, while the rest of the county was reassigned to 410.
When an area code is split, the largest city in the old numbering plan area (in this case Baltimore) typically retains the existing area code to minimize expense for changing telephone numbers. However, Bell Atlantic opted to leave the western half of the state in 301 to spare the large number of federal agencies on the Maryland side of the Washington area from the expense and disruption of a new area code. While Maryland would have likely needed another area code due to the growth of the Baltimore-Washington corridor, it is likely that a split would have been delayed had more 301 numbers been available for use in Baltimore.
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. A month later, area code 443 was assigned as an overlay for the eastern half of the state. Verizon felt overlays would be less expensive than splits that would have forced 1.2million people to change their numbers. At the time, it was predicted that it would take until 2008 to exhaust area code 240.
A September 2022 study projected that the 301/240 numbering plan area (NPA) would suffer central office code exhausted between April and June 2023. Area code 227 was already approved as an all-services distributed overlay since January 3, 2001 for the 301/240 NPA. The new area code went into service on June 14, 2023, at which time activation of new central office codes could begin, once all assignable central office codes in 240/301 had been exhausted.
The numbering plan area 301/240/227 includes all of Allegany, Charles, Garrett, Montgomery, Prince George's, St. Mary's and Washington counties, most of Frederick County, western Howard County, and slivers of southwestern Carroll County and western Anne Arundel County.
Local calls require ten-digit dialing (area code + number, leading "1" is not required). Some areas, such as Rockville, Gaithersburg, Upper Marlboro, Bethesda and Landover in Maryland remain a local call to the District and Northern Virginia.