Academic contributions to debates on migration policy tend to focus on the sovereign state controlling borders and managing cross-border movements to vouchsafe the nation’s economic, social and security interests. Irregular migrants contest this fundamental aspect of sovereignty, and states respond by defending their borders ever more fiercely as more people move in search of safety and livelihood. This article shifts the attention to the borders inside the sovereign state, where substate level of government exercise significant devolved powers and responsibilities. Once the irregular migrant has arrived, it is largely the sub-state governments’ responsibility to manage and integrate them, and sub-state economic, social and political interests come into play. This article examines some sub-state political institutions that have shown a willingness and capacity to challenge the territorial exclusivity of sovereign states in regard to migration. They do this variously by portraying irregular migrants as assets to the regional society and economy; invoking international human rights agreements and conventions; and asserting their devolved responsibilities in policy areas that enable irregular migrants to remain. This argument is supported by two Australian and two European case studies based on an analysis of parliamentary discourses and policy documents.