How many people in this US actually have ancestry within the US?

NONE - if you really think about it.

Other than Native Americans all other Americans descended from some other country. If you mean African Slaves that did not originate in the US, and only a small percentage of black people can trace their ancestry before about 1850.

My husband can trace his ancestors back to the 1600s in the U.S., but they lived in New England and they never owned slaves. Even many Southerners back then were poor farmers and never owned slaves.

the ONLY people in the US who could qualify like that is Native Americans.

No black or white people suddenly developed here as far as I know.

everyone not a Native American can trace ancestry to another country I can trace to the English Midlands, Scotland, a Channel Island, and the Austrian Tyrol

Only Native Americans have researchable US ancestry..... slaves can't research their ancestry as they were treated as 'goods'/owned property not people, everyone else in the US has ancestry from elsewhere however few are likely to be able to research and prove that ancestry from prior to US records

Except for Native Americans, everyone's ancestry traces back to another country.

I don't see how having grandparents that migrated makes your ancestry much more American than having parents that migrated but anyhow .... maybe this site will help ... https://www.usa.gov/statistics

mine goes back on my dads side to a Irish immigrant who lived in Massachusetts and him or one of his relatives owned breeds hill where the battle of bunker hill was actually fought on and another ancestor of mine was a soldier for George Washington and on my moms side is Daniel Boone lineage that has some Cherokee, partially i have ancestry that has always lived in america and the other part hasn't