We empirically study the genealogical trees of ten families for about five centuries in Korea. Although each family tree contains only the paternal part, the family names of women married to the family have been recorded, which allows us to estimate roughly the family name distributions for the past five hundred years. Revealed is the fact that the unique Korean family name distribution, characterized by a logarithmic form of the cumulative distribution and an exponentially decaying rank-size plot often called the Zipf plot, has remained unchanged for a long time. We discuss the implications of our results within a recently suggested theoretical model and compare them with observations in other countries in which power-law forms are abundantly found.