Theddlethorpe comprises two close villages and civil parishes, Theddlethorpe St Helen, and Theddlethorpe All Saints, in the East Lindsey district of the county of Lincolnshire, England. These two villages have operated as one entity for many years. They are situated approximately north from Mablethorpe and on the coast of the North Sea.
A section of the seashore of the village is part of the Saltfleetby-Theddlethorpe Dunes National Nature Reserve, which comprises sea dunes and both saltwater and freshwater marshes. The reserve is one of only five locations in the UK where the natterjack toad can be found.
Theddlethorpe St Helen has a primary school.