Frederick City Area Code List
| Area Codes | Country | State | City | Time Zone | Operating |
|---|---|---|---|---|---|
| 240 | US | Maryland - MD | Frederick | Eastern | Details |
| 301 | US | Maryland - MD | Frederick | Eastern | Details |
| 303 | US | Colorado - CO | Frederick | Mountain | Details |
| 580 | US | Oklahoma - OK | Frederick | Central | Details |
| 605 | US | South Dakota - SD | Frederick | Central / Mountain | Details |