The Saint John Valley (SJV) is an international region at the intersection of three geopolitical units: northern Maine in the US and two Canadian provinces (northwestern New Brunswick and eastern Quebec). The US side of the SJV is home to a francophone community which, due to geographic isolation and its proximity to francophone Canada, has been able to persist as a relatively hermetic enclave of French speakers, whose variety is the product of contact among Acadian French, Quebec French (or Laurentian French), and English. However, the French in Maine’s SJV has historically lacked the institutional support of its Canadian counterparts and has existed primarily in the oral domain. Furthermore, as the result of oppressive language policies, negative language attitudes, and the progressive Americanization of the region over the course of the 20th century, local French has been undergoing shift to English, especially since WWII. Today it is a steeply declining heritage language as older fluent speakers are dying without (fully) transmitting French to younger generations, who are increasingly English-dominant. This gradual shift to English has produced a proficiency continuum that is roughly age-graded, with speakers of different generations varying in fluency, grammatical mastery, and overall functional capacity in French. This dissertation examines the structure of the French in Maine’s SJV, specifically with regard to irrealis mood in the verbal system (future, conditional, and subjunctive) with the objectives of first establishing the fluent speaker norm and then determining how less proficient speakers deviate from it. The study finds significant qualitative differences in the French of speakers across a proficiency continuum, with several variables within irrealis mood providing evidence for this continuum. If the fluent speaker norm mirrors that of other North American French varieties with respect to irrealis mood, particularly Laurentian varieties, less proficient speakers exhibit increasing difficulty and variability in their production of the structures characterizing this mood, with the result that they are often unable to reliably encode for semantically meaningful distinctions. Even when semantics are not clearly compromised, French in the SJV manifests traits that are consistent, if not necessarily synonymous, with language death.