Area codes 240 and 301

North American area codes 240 and 301 are telephone area codes for the western half of Maryland. They serve Maryland's portion of the Greater Washington, D.C., metro area, portions of southern Maryland, and the more rural areas in the western portion of the state. This includes the communities of Cumberland, Frederick, Hagerstown, Gaithersburg, Rockville, Landover and Silver Spring.

The main area code, 301, was one of the original area codes established in 1947, and originally covered the entire state of Maryland. This was somewhat unusual, given that Maryland is home to two very large metropolitan areas, Baltimore and the suburbs of Washington, D.C. The North American Numbering Plan Administrator wanted to keep the number of "clicks" to a minimum for densely populated areas given the rotary dialing technology in use at the time. Codes with as few as five clicks were possible for area codes covering just a city or portion of a state under NANPA's original guidelines (0 and 1 were not allowed as the first digit, the second digit was either 0 or 1, and the third digit could not be the same as the second digit). However, area codes covering an entire state always had 0 as the middle digit, for a minimum of 13 clicks. Taking Maryland's density into account, NANPA assigned it an area code with 14 clicks (3+10+1), tied with the District's 202 as the second-fastest single-state area code that could be dialed under NANPA's original guidelines (behind New Jersey's 201).