There are a lot of hot spots on this map:
* https://www.lightpollutionmap.info/
For the US, one-third of the population lives in coastal counties:
* https://www.census.gov/library/stories/2019/07/millions-of-a...
Two-thirds of the US population lives within 100mi (160km) of the border:
* https://www.aclu.org/other/constitution-100-mile-border-zone
While I haven't been engaged in amateur astronomy for a long time, I vaguely remember an event/meeting years ago that was not that far out in the country, and just a few miles/minutes travel away from the "strip malls" made a huge difference. Northern lights were visible and I think the Milky Way.
I have been out west where it is really dark, so whether or not my recollection is accurate, I do know what undisputedly dark skies are like.
It's about 180 km (110 miles) to merely get into a light blue spot for me, and it's actually a quite short distance compared to country's average.