In the study of dialect geography, boundaries of many types appear at the edges of dialects (ANAE, Dinkin 2013). However, the disruption of a dialect boundary at a single point by a non-linguistic change does not necessarily change the dialect boundary but creates a new type. The present study examines the influence of the Inland North dialect on the St. Louis Corridor, a geographically Midland area located between Chicago and St. Louis across the state of Illinois. The Corridor is also the home of Route 66, which in 1926 was the first paved highway in Illinois. In analyzing data from original interviews, the Atlas of North American English (Labov, Ash, and Boberg 2006), and archival resources (Wood 1996), I situate the Inland North influence in time, namely for those born in the 1920’s through 1940’s. Based on corroborating evidence from population statistics, traffic patterns, and the history of Route 66, I demonstrate a timeline for Inland North influence and how it interacts with the Midland features. I also show that the Inland North influence rises and retreats alongside a major change in transportation patterns from water to land (cf. Trudgill 1974 for a similar dialectal change). Based upon the distinctions between the findings in this study and other situations of dialect boundaries, I propose a new boundary type: a dialect “breach.”