It is estimated that at the peak of its empire, Yap proper alone has a population of about 50,000. In 1992, though, the total population of Yap State is estimated at just over 11,0041 The precipitous decline in populations is probably due in large part to the arrival of foreigners and the introduction of new diseases. The depopulation of Yap hit bottom at the end of World War II when there were just under 3,000 Yapese. High birth rates in the 1980s suggest the state is now in the midst of a new population boom (50 % of the current population is under 20 years old).
There are four distinct languages indigenous to Yap State – Yapese, Ulithian, Woleian. and Satawalese – and some theorists point to the distinct languages as evidente that the people of Yap and the Outer Islands are descendants of different ancient migrating societies. According to this theory, the Yapese people may be descendants of an ancient Indonesian or Philippine culture, and the Outer Island people descendants of a Melanesian or Polynesian culture.