Favorite U.S. Tax Haven of Rich and Powerful Holds $500 Billion

There’s no telling where the vast fortunes hide on tree-softened Phillips Avenue here in Sioux Falls.

No billionaires in Brioni tuck into the gravy-drenched roast beef sandwich at the Diner. No dark-windowed Escalades cruise past the Child’s Play Store, where the owner sports a pin that proclaims her a “glow getter.”

Photographer: Anders Melin/Bloomberg

Yet the money is here, mind-boggling sums of it, along this avenue in South Dakota, as the wider world discovered one sunny Sunday in October.

Somehow, millions of private financial records — known as the Pandora Papers — had landed in the hands of journalists. They laid out ...