Wikia

The Sea
Location information
Permanent residents	Dursley family (formerly, briefly) ; Harry Potter (formerly, briefly) ;
Affiliation	Hut-on-the-Rock ; England (presumably) ;

"Mr H. Potter,
The Floor,
Hut-on-the-Rock,
The Sea."

The Sea is a body of salt water that borders with English coastline. The Hut-on-the-Rock is located on a small island found on it.^[1]

Behind the scenesEdit

England has shores on two seas and partly one ocean: the Irish Sea, North Sea, and Antlantic Ocean plus English Channel to the south.^[2]^[3] Given the fact that county of Surrey lies in south-eastern part of England, the sea on which the rock with the hut is placed might refer either to North Sea or English Channel.
It is unknown whether the name of the sea is not specified in Harry's acceptance letter. The most probable reason is that J.K. Rowling, targeting her first book about Harry Potter to relatively young audience, didn't want to include a name such as 'English Channel' from the fear that children would hear it the first time, because of the little age. Another reason is the possiblity of wizards' trifle knowledge on geography (not being taught at schools like Hogwarts), though it's unlikely.

The Sea

Location information
Permanent residents	Dursley family (formerly, briefly) Harry Potter (formerly, briefly)
Affiliation	Hut-on-the-Rock England (presumably)