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 frauð which means "manure" and the meaning would then be "the fertilized field" (see also Frogner and Tøyen).
Prior to 1889, the name was written "Fron". Between 1837 and 1865, the name of the municipality was Drøbak landdistrikt.[4]
Coat-of-arms
The coat-of-arms is from modern times. They were granted on 20 May 1988. The arms symbolize the Oscarsborg Fortress in silver on a blue background. The fortress is on the Drøbaksund in the Oslofjord in the municipality. The fortress was built in the late 19th century and played a major role in the defence of Norway in the beginning of World War II.[5]
Number of minorities (1st and 2nd generation) in Frogn by country of origin in 2017[6]