Mellette is located at (45.153970, -98.498336).
There were 90 households out of which 43.3% had children under the age of 18 living with them, 58.9% were married couples living together, 4.4% had a female householder with no husband present, and 30.0% were non-families. 27.8% of all households were made up of individuals and 15.6% had someone living alone who was 65 years of age or older. The average household size was 2.76 and the average family size was 3.44.
In the city the population was spread out with 35.5% under the age of 18, 5.6% from 18 to 24, 26.2% from 25 to 44, 18.1% from 45 to 64, and 14.5% who were 65 years of age or older. The median age was 34 years. For every 100 females there were 100.0 males. For every 100 females age 18 and over, there were 107.8 males.
The median income for a household in the city was $34,107, and the median income for a family was $34,500. Males had a median income of $30,521 versus $19,375 for females. The per capita income for the city was $11,467. About 10.9% of families and 12.6% of the population were below the poverty line, including 9.9% of those under the age of eighteen and 28.6% of those sixty five or over.