The 2000 census reported that Frankfort had a population of 27,741, of whom 14,513 were female and 13,228 were male. Census Bureau estimates of the city's population from 2001 through 2005 are shown in the following table:

Frankfort residents' median age, according to the 2000 census, was 35.9 years. Of the 18,458 people 25 years of age or older, 14,616 had at least a high school diploma, and 4,594 had a bachelor's degree or higher. Per capita income (in 1999 dollars) was $20,512; median family income was $47,855 (again in 1999 dollars).