It is tempting to look on it as a village, probably actually of Aylesbury, but given it does have its own town government, with selectmen, a justice of the peace and a constable, I think we must assume it is probably meant to be a town in its own right. Just a forgotten and decaying one.
I think these sorts of places (Innsmouth too) always cause problems in the modern (and even the early 20th century) world. Do such isolated, decaying places still exist in civilised areas? The Severn Valley is even sillier, in fact. It's just not really possible for such places to exist in modern England. Too much infrastructure (e.g. policing, which is on a county basis in Britain, not a local basis).
Bolding of your quote is mine.
This is why I suggested upthread a migration further west in the United States if the keeper wants to maintain the isolation. Central and Western Massachusetts might be rural suburbia as opposed to urban suburbia of eastern Massachusetts but it is still much more suburban than rural. For something like Dunwich in the story in today's US, the location needs to be moved further west. Kentucky (as seen above) or Tennessee might work but for really small towns even further west is probably better. For instance, when in Wyoming and Montana, I saw towns of 200 people and the distance between them was so significant there were signs on the highways reminding people that there were not gas stations for say, the next 100 miles.
Edited by Mysterioso, 04 October 2017 - 03:04 PM.