94-year old Holocaust survivor, Yitta Schwartz, leaves 2500 descendants:
She had 17 children herself, and 170 grandchildren. By my reckoning, each of her grandchildren would have an average of 13.7 descendants, and apparently they have grandchildren themselves. It hardly seems possible. The Guinness world record as of 2002 was 824, from one Samuel Mast who died in 1992 at age 96 in the US.
She was living at Kiryas Joel, a Hasidic community in lower New York. Wikipedia says that it has the lowest median age (15 years), highest concentration of Hungarians (19%) and the highest poverty rate (2/3) of any community in the nation. The 2500 number is probably apocryphal, but is kind of awe-inspiring.