Yeah, I was surprised by it when I first looked it up also. I think partly because most people who are demographically similar to me are on private health insurance, so I think of the US as having mostly a private system. But a little over 40% of the U.S. population has public coverage: 20% are on Medicaid or CHIP (lower-income), 18% Medicare (age 65+), and 5% military/veteran.