This paper presents a new perspective on the origin and development of the Mary-merry-marry merger, the conditioned merger, or neutralization, of mid and low front vowels before /r/ in dialects of North American English. The city of Montreal, Quebec represents one of very few regions in which this merger has not taken hold, despite the fact that a near-complete merger is found in the nearby rural region of Quebec’s Eastern Townships. This paper attempts to shed light on this puzzling geographic distribution using data from archival interviews conducted with Eastern Townshippers born between 1895 and 1915. An acoustic analysis of the vowels before /r/ is presented and compared with data from recent studies of Montreal English. Acoustic analysis of the mean values of the first and second vowel formants shows a great deal of variation in these speakers’ productions of the historically low front vowel before /r/. In some tokens it is clearly merged with the mid vowel, while in others the two phonemes remain clearly distinct. Further, this variation is found both between speakers and in the speech of individuals themselves. Although not entirely homogenous, the speech community does appear to share general norms with regard to which words are or are not merged. These results demonstrate that the merger was not a lexically abrupt sound change. Rather, the results are consistent with a theory of sound change via lexical diffusion, which implies a much longer timeline for this change than previously assumed, suggesting its origins may go back many more generations. As such, it is suggested that the current geolinguistic pattern of the merger may be traced to the different settlement histories of Montreal and the Eastern Townships.