In the first half of the seventeenth century, several foreign plantations were established on wetlands drained during a wave of ambitious state-led projects across eastern England. The lines of solidarity and separation forged by this little-known episode in the history of migration pose important questions about how emergent notions of nationhood intersected with local and transnational, religious and economic communities. This article investigates the causes and consequences of the settlement of Calvinist refugees on drained commons in Hatfield Level. It argues that fen plantation expands understanding of the relationship between English agricultural improvement and imperial expansion in the British Atlantic, as migrant communities acted in the service of empires and states while forging transnational Protestant networks. As Calvinists and cultivators, however, the settlers were met with hostility in England. While the crown encouraged foreign plantation as a source of national prosperity, Laudian church authorities identified it as a threat to religious conformity, the state, and society, muddying depictions of English governors as guarantors of refugee rights. Local efforts to violently expel settlers from Hatfield Level, meanwhile, were rooted in fen commoners’ defense of customary rights, as parallel communities sought to enact rival environmental and economic models. The settler community interpreted these experiences through the lens of transnational Protestant adversity, entangling their quest for religious freedoms with their remit as fen improvers. Moving beyond dichotomous arguments about xenophobia, this article traces the transnational imaginaries, national visions, and emplaced processes through which collective identities and their sharp edges were constituted in early modern England.