I'm sure that a sizeable percentage of Americans own a significant amount of shares via 401k or whatever, but it feels surprising if 1 in 10 own more than 1% of a company, because all of those people holding shares as investments will be buying shares in companies with thousands or millions of other investors.

But maybe it's true - I just googled about the US has 340m people and 32.5m companies - so the majority of them must be small (population/number of companies). And while a lot of companies will be owned by the same people or just administrative divisions of a group of companies, most companies have multiple directors so maybe on average it does balance out to 1 in 10 owning a decent chunk of a company. It just feels like a surprising fact.

This site [1] has some interesting stats on size of businesses, although it's interesting that in 2019 these figures say there were less than 8m businesses, which disagrees with what google told me. Also says over half of US companies have 0-4 employees.

[1] https://paradoxesinc.com/resources/us-business-patterns/