Theddlethorpe St Helen or East Theddlethorpe is a village and civil parish in the East Lindsey district of the county of Lincolnshire, England. It lies about 3 miles (5 km) north of Mablethorpe on the North Sea coast. Some seashore belongs to Saltfleetby-Theddlethorpe Dunes National Nature Reserve, consisting of sea dunes and saltwater and freshwater marshes. It is one of five UK locations where the natterjack toad is found. In 2011 the parish had a population of 525. The parish touches Gayton le Marsh, Mablethorpe and Sutton, Theddlethorpe All Saints and Withern with Stain. Theddlethorpe St Helen shares a parish council with Theddlethorpe All Saints.