[8] According to the United States Census Bureau, the city has a total area of 1.63 square miles (4.22 km2), all of it land.

[9] The 2020 United States census counted 1,313 people, 584 households, and 348 families in Harper.

There were 741 housing units at an average density of 456.6 per square mile (176.3/km2).

35.6% of households consisted of individuals and 18.2% had someone living alone who was 65 years of age or older.

[15] The percent of those with a bachelor’s degree or higher was estimated to be 7.1% of the population.

[19][20] As of the census[21] of 2010, there were 1,473 people, 624 households, and 385 families living in the city.

There were 742 housing units at an average density of 455.2 per square mile (175.8/km2).

34.5% of all households were made up of individuals, and 15.4% had someone living alone who was 65 years of age or older.

There were 787 housing units at an average density of 612.2 per square mile (236.4/km2).

35.3% of all households were made up of individuals, and 18.1% had someone living alone who was 65 years of age or older.

The community is served by Chaparral USD 361 public school district.