According to the United States Census Bureau, the town has a total area of 0.3 square miles (0.7 km²), all of it land.
Harrold has been assigned the ZIP code 57536.
There were 83 households out of which 33.7% had children under the age of 18 living with them, 55.4% were married couples living together, 2.4% had a female householder with no husband present, and 39.8% were non-families. 37.3% of all households were made up of individuals and 22.9% had someone living alone who was 65 years of age or older. The average household size was 2.52 and the average family size was 3.46.
In the town the population was spread out with 32.1% under the age of 18, 5.3% from 18 to 24, 28.2% from 25 to 44, 17.7% from 45 to 64, and 16.7% who were 65 years of age or older. The median age was 35 years. For every 100 females there were 91.7 males. For every 100 females age 18 and over, there were 94.5 males.
The median income for a household in the town was $27,083, and the median income for a family was $36,071. Males had a median income of $29,375 versus $21,667 for females. The per capita income for the town was $14,725. About 6.0% of families and 8.8% of the population were below the poverty line, including 5.1% of those under the age of eighteen and 22.2% of those sixty five or over.