Billionaire's Report

UBS claims there are 2158 billionaires as of last year. Their wealth increased by an average of $648 million during 2017 to an average total of $4.1 billion each.

Update (October 31):  The Guardian reports that the three wealthiest U.S. families, the Waltons, the Mars, and the Kochs are worth a combined $348.7 billion.

Since 1982, these three families have seen their wealth increase nearly 6,000%, factoring in inflation. Meanwhile, the median household wealth went down 3% over the same period.