This article was motivated by a claim in literature that migrants are ruralising Third World cities. It investigates the impacts of migration - the fact that all residents are from somewhere else - on the form and function of an informal settlement, using an illegal shantytown in Mamelodi, Tshwane, as a case study, by exploring the relationships between (1) the demographic profiles of migrant households, including their origins and expectations, (2) the form of a squatter settlement, and (3) how it actually functions as a setting for social and economic activities. Illegal settlement making is finally tentatively explained with a theory developed from the ruralisation hypothesis.