Frankfort, SD has a population of 98 and is the 26,988th largest city in the United States. The population density is 124 per sq mi which is 1051% higher than the South Dakota average and 37% higher than the national average. The median age in Frankfort is 53 which is approximately 43% higher than the South Dakota average of 37. In Frankfort, 63% of the population over 15 years of age are married, 96% speak English and 0% speak Spanish. 83% of Frankfort residents were born in South Dakota, 13% were born out of state, 0% were born outside of the United States and 4% were foreign born.