Drawing on an ethnography of Wisconsin-based descendants of Belgian immigrants, this article explores social dynamics relating to ways lay users of genomic ancestry testing (GAT) understand genomic ancestry and how their understanding raises questions concerning the construction of their identities. The study focuses on a group that presents interesting features for which the existing literature is sparse (i.e. a rather secure Belgian ancestry/present identity, the absence of a clear ascription to the category “Belgium/Belgian” from the tests, and a biological connectedness in the Belgian community). GAT is approached as a socio-cultural object contextualized at a local level. The analysis involves specifying the discursive practices by which individuals entangle with this knowledge, following a two-pronged perspective derived from the nature of the information received by users, which is both individuating/deindividuating and deterministic/probabilistic. The paper, therefore, provides new insights into the manners in which social actors trigger their responsibility in response to genomic ancestry, and this questions the users’ sense of identity.