British Cochin was a port in southwestern India surrounded by princely states. This article uses a dispute surrounding its limits to interrogate the role international law played in generating novel forms of political claim-making among European and non-European powers at the turn of the twentieth century. Cochin was located in an area where both physical and political boundaries were hard to define. Situated at the tip of a narrow coastline surrounded by water, it was also lodged amid territories belonging to two princely states—Cochin State and Travancore. Its ever-shifting coastline and proximity to princely states forced colonial authorities to adopt a flexible approach to the port’s boundaries, allowing the tiny princely state of Cochin to become progressively more involved with the British port’s development over the nineteenth century. The article starts by examining the forces that shaped these entanglements, and then explores a territorial dispute involving British Cochin to illuminate the ways in which, during the twentieth century’s first quarter, both the colonial administration and the Cochin State deployed the language of international law to try to extend their powers over the port. By highlighting the Cochin State’s partially successful attempts at claiming sovereignty over the waters surrounding the harbor in order to become involved with the development of a port in British India, this article shows how international law emerged as a site through which semi-sovereign territories began testing and even extending the limits of their sovereignty.