According to the 2020 US Census, about 80% live in an urban area. However, the definition is not exactly what people think of when you say “urban”.
In 2020, the census lists 2,611 urban areas, including areas with a few thousand people.
https://www.census.gov/programs-surveys/geography/guidance/g...
Shouldn’t be too hard to break this down with a more colloquial definition (say, areas over 500k or 750k people). I’m just not at a real computer :)