This paper aims to show that the use and analysis of language data from the Canadian census by the various scientific and political actors have generally been carried out from the perspective of ethnicity or ancestral origin. Such an “ethnicizing” perspective has largely contributed to the social, political and scientific construction of language groups, particularly in Quebec, and to the consolidation of their boundaries. Through language data and the field of demolinguistics, this paper shows the ways in which processes of definition and categorization have occurred in relation to language groups as we know them today. Due to the significant change in the ethno-cultural composition of the population over the past forty years, the article shows that there is a need to review the traditional ethnicizing paradigm of language groups and to make room for a new paradigm focused on language and on a more inclusive measure of the diversity of identities and multiple linguistic practices.