For a little follow-up: before prohibition, there was a fair number of people making beer. Due to the sheer size of the US, this meant that there were unique varieties that began popping up, whose production was to be considered "common" for the region.
Out of all these cool styles that started off, there are only two which are officially known/recognized by the Beer Judge Certification Program (BJCP), the California "Common" (AKA: Steam beer) and recently the Kentucky "Common." (PDF)
One beer that is not recognized by the BJCP, but is known of is something called a "Pennsylvania Swankey," which in itself is a low-alcohol malt beverage flavored more with anise than hops, possibly even resembling a hard root beer.
But as far as common (heh) knowledge is concerned, those are the only three regional/"common" beers that people tend to know of. For the size of the US, there's got to be a little bit more floating around out there. A New York Common, a Virginia Common, something. Would anybody know of any other styles? Where would one start looking?
You'll likely get more answers over in r/beer. But I can tell you as much as I know as a professional in the beer industry.
In order to earn a spot as a separate style, there needs to be something that clearly distinguishes it from other styles. There's no reason to create a "New York Common," "Virginia Common", etc. style if those styles are all basically the same beer. So while there was plenty of beers being brewed in America, they mostly were based on either the most popular European styles, or were American standard lagers or steam beers.
I can think of a few beers here in Minnesota that are based on pre-prohibition recipes. Much beer in the Midwest was brewed by German-Americans, and based on the German pilsner style. However, they had a tendency to use a significant amount of maize in the mash. Schell's Deer Brand is based on their original pre-prohibition recipe using 30% maize. 612 Brewery's Gateway Park is similar. However, these are technically just examples of "American standard lager," same as today's Bud or Coors. But while it's the same style, the recipes are pre-prohibition.
I've also had a style at Red Wing Brewery called Remmler's Royal, made from a 1986 recipe - a much more robust flavor. To my taste, it is basically a California common.
Moreover, a new brewery is resurrecting Minnesota's "first" beer, which again seems to fall in the California common style.
Most historical beers fit into one of the BJCP styles, so you may not discover a new one. But if you look in the current craft beer world, you'll discover many historical recipes to try.