Duncan, Iowa

As of the census of 2020,^[9] there were 57 people, 32 households, and 23 families residing in the community. The population density was 72.6 inhabitants per square mile (28.0/km²). There were 32 housing units at an average density of 40.7 per square mile (15.7/km²). The racial makeup of the community was 98.2% White, 0.0% Black or African American, 0.0% Native American, 0.0% Asian, 0.0% Pacific Islander, 0.0% from other races and 1.8% from two or more races. Hispanic or Latino persons of any race comprised 0.0% of the population.

Of the 32 households, 37.5% of which had children under the age of 18 living with them, 68.8% were married couples living together, 9.4% were cohabitating couples, 3.1% had a female householder with no spouse or partner present and 18.8% had a male householder with no spouse or partner present. 28.1% of all households were non-families. 21.9% of all households were made up of individuals, 9.4% had someone living alone who was 65 years old or older.

The median age in the community was 48.3 years. 17.5% of the residents were under the age of 20; 1.8% were between the ages of 20 and 24; 26.3% were from 25 and 44; 24.6% were from 45 and 64; and 29.8% were 65 years of age or older. The gender makeup of the community was 63.2% male and 36.8% female.

Duncan is a part of the Garner–Hayfield–Ventura Community School District. It was previously in the Garner–Hayfield Community School District,^[10] which merged into the current GHV district on July 1, 2015.^[11]