Non-rhoticity is associated with two quite distinct social groups in the south[.] ‘[…] The fact […] has been either over-looked or deliberately ignored’, complains McDavid (1948), in an article reporting his investigations into rhoticity and non-rhoticity in South Carolina.
Source: wiktionary
In the present analysis, we coded for the variants [ɹ], [ʁ], [ɾ], [ʋ], and [ɹ̝], and the zero variant [∅] to indicate non-rhoticity in postvocalic positions[.] […] Non-rhoticity appears to be (near-)categorical for all speakers.
Source: wiktionary
It is surely not a coincidence that non-rhoticity developed in North America along the East Coast. […] In no case did it spread very far inland, except in the case of speakers of African American Vernacular English, who migrated from the southeast to the rest of the country many decades later, taking their non-rhoticity with them.
Source: wiktionary
The discussion on when and how non-rhoticity began to spread in England is also relevant for the reconstruction of the development of non-rhoticity in North America.
Source: wiktionary