Dorchester is an unincorporated community in northwestern Allamakee County, Iowa, United States. It lies along local roads just off Iowa Highway 76, north of the city of Waukon, the county seat of Allamakee County. Its elevation is 738 feet (225 m). The town was originally settled by Harvey Bell and Edmund Bell, and was named after Dorchester, England. Although Dorchester is unincorporated, it has a post office, with the ZIP code of 52140, which opened on 21 May 1857. Dorchester is located in Waterloo Township.