There’s linguists who believe that some American Southern accents are closer to 1776 British speech than modern British accents are.
Several years ago it was a documentary about the development of the English language throughout history. I think it was this one:
https://en.m.wikipedia.org/wiki/The_Adventure_of_English
There was a mention of an island I believe in South Carolina where there had been more limited interchange with surrounding areas over the years and the accent stated pretty much the same in the last couple of hundred years. The narrator said that this accent was probably closer to what the British spoke during the revolution than the British themselves today. I did not see this shown on the episode list, but I’m pretty sure that this was the series I remember.