Reddit mentions of Encyclopedia of World Cultures, Vol. 1: North America

I know there's a sizeable population in Augusta, South Carolina. That's only based on anecdotal evidence.

Other than that there are Travellers' Camps in Ohio, Mississippi, Georgia, and Texas. I'm not too educated on the subject, so that list is according to Wikipedia which sources this. It seems the history of Irish Travellers and Cant in The US isn't very well documented, but they're certainly present here.

EDIT: Miss Mary Elizabeth Andereck seems to be the sole authority on the topic, but her writings are hard to find (other than the one linked above). I've found two other bits, but just Google listing that they exist, can't find where you could get them, or anything else about the author: 'Irish Travellers in a Catholic Elementary School' (no clue what this book is quite about other than what the title infers) and 'Ethnic Awareness in The School: An Ethnographic Study': "a detailed study of `gypsies' in the American South"

EDIT II: Oh! Here's Ethnic Awareness and The School on Amazon.