Duncan is a census-designated place (CDP) in Hancock County, Iowa, United States.

There were 32 housing units at an average density of 40.7 per square mile (15.7/km2).

Hispanic or Latino persons of any race comprised 0.0% of the population.

21.9% of all households were made up of individuals, 9.4% had someone living alone who was 65 years old or older.

This article about the geography of Hancock County, Iowa is a stub.