Diamondhead Lake is an unincorporated community and census-designated place in Penn Township, Guthrie County, Iowa, United States.

As of the census of 2020,[3] there were 371 people, 154 households, and 117 families residing in the community.

There were 226 housing units at an average density of 232.3 per square mile (89.7/km2).

Hispanic or Latino persons of any race comprised 2.4% of the population.

21.4% of all households were made up of individuals, 9.7% had someone living alone who was 65 years old or older.