Sloshspot has compiled a list of the 10 oldest bars in the US and it's pretty cool, even if the writers did accidentally overlook about half the actual oldest bars in the US (including The Horse You Came in On in Fells Point).
Also not mentioned: Reynold's Tavern in Annapolis. Maybe it doesn't count because only the Sly Fox part of it is really bar-like?
Regardless, it's a cool list and the motivation behind it (the author was drinking in a pub in Europe and naturally started thinking about how young everything is in the US...so he looked around for some of our not-so-young places).
I've never lived very far from pretty intensely colonial areas, so I thought I had a decent appreciation for history - until I went to Europe for the first time. That said, our history is pretty great. So why not absorb a little of it while you drink?