| Area Code | 240 |
| State | Maryland |
| Current Time in Area Code 240 | 240> EDT |
| Timezone | Eastern Daylight Time |
| Regional Market Area | Hagerstown Area Metro DC Morgantown Area |
| Metro Area(s) | California-Lexington Park, MD |
| Population (2020) | 2832990 |
| Adjacent Area Codes | 202,227,301,304,410,443,540,571,582,667,681,703,717,724,757,771,804,814,826,878,948 |
| Allegany County |
| Charles County |
| Frederick County |
| Garrett County |
| Montgomery County |
| Prince Georges County |
| Saint Marys County |
| Washington County |
| Aspen Hill |
| Bethesda |
| Bowie |
| Chillum |
| Clinton |
| College Park |
| Frederick |
| Gaithersburg |
| Germantown |
| Hagerstown |
| Montgomery Village |
| North Bethesda |
| Olney |
| Potomac |
| Rockville |
| Silver Spring |
| Waldorf |
| Wheaton |