Frogn is a municipality in Akershus county, Norway. It is part of the Follo traditional region. The administrative centre of the municipality is the town of Drøbak. Frogn was established as a municipality on 1 January 1838 (see formannskapsdistrikt). The city of Drøbak was merged with Frogn on 1 January 1962.
Frogn is located at the southern part of the peninsula between the main Oslofjord and Bunnefjorden. It borders Nesodden, Ås and Vestby.The municipality (originally the parish) is named after the old Frogn farm (Old Norse: Fraun), since the first church was built here. The name must be very old and the meaning is unknown. One theory is that it is derived from the Norse word frauđ which means "manure" and the meaning would then be "the fertilized field". Prior to 1889, the name was written "Fron".Between 1837 and 1865, the name of the municipality was Drøbak landdistrikt.