From my understanding of Tolkien’s work, a lot of the place names he used were extrapolated from areas of merry old England such as the Shire being a reference to Devon (Devonshire and as a matter of fact many older folk in Devon actually refer to it as being the “shire”) which anyone who has been there can attest would be the inspiration for the Hobbit homeland. I would guess Frog Morton would be an iteration of Frogmore House. I have no proof, but read enough of his work and about his life it seems more reasonable than not.