ABSTRACT Why do South Africans demonstrate such high levels of immigrant population innumeracy? This tendency to overestimate the number of immigrants in one’s country has been linked to consequences, including support for anti-immigrant legislation and participation in xenophobic violence. Some have called for disseminating accurate information as a means to reduce anti-immigrant hostility. However, most of what we know about innumeracy comes from research in the Global North, and it remains unclear whether it operates similarly in other parts of the world. Thus, the current study seeks to understand innumeracy as it exists in South Africa with the goal of informing efforts aimed at improving perceptions and reducing tensions. Using patterns established in the existing research and logic based on the cognitive availability and affect heuristic processes, the current study compiles a list of possible correlates and tests their effectiveness for understanding South Africans’ misperceptions. The analysis also goes beyond replication by examining a wide array of cognitive availability factors, many of which have not been considered in previous innumeracy research. Overall, findings from the 2019 South African Social Attitudes Survey identify several predictors of immigrant population innumeracy, some which are unique to South Africa. In particular, relational information channels, like friends, family, and local leaders, have a much larger impact on perceptions than non-relational media channels, like television and the Internet. These new insights into the innumeracy phenomenon as it exists in South Africa may prove useful for designing targeted interventions to encourage more accurate perceptions.