Dersingham is a village and civil parish in the English county of Norfolk. It is situated some 12 kilometres (7.5 mi) north of the town of King’s Lynn and 70 km (43 mi) north-west of the city of Norwich, opening onto The Wash. ~Wikipedia.
Miss Alice Maude Beckett was the Postmistress here in or around 1900, according to Kelly’s Directory. I assume the post office was one of these buildings.
