At the end of the 19th century, numerous St. Petersburg residents established their summer homes in the Karelian Isthmus, a picturesque region in the Grand Duchy of Finland, an autonomous province of the Russian Empire. The ease of travel between the Russian imperial capital and the Finnish seaside towns contributed to this practice. After 1917, a new border regime delineated the nascent Finnish state from the equally new Russian/ Soviet state. This change displaced the majority of Russian proprietors, as well as those imperial subjects who rented vacation properties from local Finns. This article addresses how state-building practices distinguishing between insiders’ and outsiders’ access to rights and privileges reflected the significance of territorial borders as markers of a state’s territorial sovereignty. It does so by investigating how Finnish–Russian social ties affected the Finnish government’s management of real estate owned or used by subjects of the former Russian Empire. Using archival material from the Administrative Organ for Property of Foreign Owners in Viipuri Province (Finland), this article examines how property settlements decisions had unintended consequences when officials attempted to balance state and individual interests. These decisions in turn challenged the primacy of the territorial border as an institution that separates insiders from outsiders.