Using a corpus of synchronic dialects from England, Scotland and Northern Ireland (the Roots Archive), this paper presents a quantitative distributional analysis of a series of morpho-syntactic changes: verbal -s (1), causal conjunctions (2), relative clauses (3), the modals of necessity (4), stative possessive meaning (5), and future temporal reference (6). While the dialects sometimes differ in their favoured variant, internal linguistic constraints are typically shared. These can often be traced to the history of English, and can be interpreted as persistence. On the other hand, cross-dialectal differences, particularly in terms of regional diffusion and social embedding, reveal that the changes are not progressing at the same rate. Indeed, each community represents its own ‘slice in time’. Such findings illuminate how internal grammatical constraints and external factors conspire in the ebb and flow of linguistic change; dialect corpora can provide useful insights into these processes.