The category of population is central to large-scale medical research, yet it may be defined in various ways. This chapter engages with the Million Death Study, an effort to generate more reliable and representative causal mortality statistics in India, to show how a population gets defined in terms of data. It discusses how, in response to shortcomings attributed to India’s medical system, population gets defined in terms of a demographic population sample, to which the interview method of verbal autopsy is attached to produce symptomatic data. The chapter then traces the processes through which descriptions of symptoms are analysed to arrive at individual causes of death and how these causes get aggregated to represent the population in terms of cause-specific mortality statistics. Such statistics do not only represent India in a particular form (that, e.g., includes regional differences), but also render it an exemplar for the global South. At the same time, due to the lack of clinical confirmation, limitations to diagnostic accuracy are accepted in light of the expected contribution study data can make to improvements in public health. The Million Death Study thereby shows different ways of assembling a population through data and their consequences.