Hamill is located at (43.595447, -99.682586).
According to the United States Census Bureau, the CDP has a total area of 1.2 square miles (3.2 km²), of which, 1.2 square miles (3.2 km²) of it is land and 0.04 square miles (0.1 km²) of it (2.40%) is water.
Hamill has been assigned the ZIP code 57534.
There were 5 households out of which 20.0% had children under the age of 18 living with them, 40.0% were married couples living together, and 40.0% were non-families. 40.0% of all households were made up of individuals and 20.0% had someone living alone who was 65 years of age or older. The average household size was 2.20 and the average family size was 3.00.
In the CDP the population was spread out with 18.2% under the age of 18, 27.3% from 25 to 44, 9.1% from 45 to 64, and 45.5% who were 65 years of age or older. The median age was 62 years. For every 100 females there were 83.3 males. For every 100 females age 18 and over, there were 80.0 males.
The median income for a household in the CDP was $42,500, and the median income for a family was $42,500. Males had a median income of $15,000 versus $16,250 for females. The per capita income for the CDP was $11,833. None of the population or families were below the poverty line.