The census definition of "urban" is kind of absurd. If I'm reading it right, living in a town of 2500 is "urban." If I'm reading it wrong, living in a town of 50,000 is "urban." Either way, you'd likely consider a lot of that 80% rural.

Where is that definition from?

The 2020 census proposes using "385 housing units per square mile as the primary criterion for determining whether a census block qualifies for inclusion in an urban area". Previously it was 1000 people per square mile (or equivalent to the above with 2.6 persons per household).

https://www.federalregister.gov/documents/2021/02/19/2021-03...

Note that's only in the "proposed changes section, and that there is still much more information in that document. That change seems to determining how much of a town is an urban tile, but is not the primary designation of urban.

I guess density is the real measure.