For almost half a century social scientists have explored the phenomenon of chronic illness. In this paper, I examine how the concept of chronicity participates in present‐day mental health care settings. Using ethnomethodology and material‐semiotic theory within science and technology studies, I investigate how the classification ‘chronically mentally ill’ interacts with the everyday socio‐material shaping of public mental health care in the context of professional institutions. Drawing on ethnographic fieldwork in a psychiatric day hospital and in a community day care centre in Berlin, Germany, I demonstrate how the classification of chronicity acts as a tool of description (of people or their conditions), regulation (of therapy, health care or administration), and connection to infrastructures of care (practised technologies or standards of various kinds). In these ways, I argue, the classification engages in actions of producing treatability, arranging resources, demarcating responsibilities, practicing accountability, and doing presence. Notably, community mental health care has developed into a designated territory of the concept: explicitly arranged for ‘the chronically mentally ill’ as a human kind, we can take everyday life in these institutions as instructive of how chronicity is defined in daily practice.