In a landmark ruling, the Supreme Court of the United States determined that Ellis Island is primarily part of New Jersey. This decision concluded a long-standing dispute between New Jersey and New York over jurisdiction of the island, which has historical significance as a gateway for immigrants to the United States from 1892 to 1954. The case 'New Jersey v. New York' stemmed from conflicting assertions regarding the boundaries of Ellis Island that were shaped by a treaty signed in 1834. The complexities in the legal framework resulted from the island's landmass, which had been altered over time through landfill expansion.

Ellis Island originally consisted of a small landmass, but extensive renovations and construction in the late 19th and early 20th centuries added considerable size, raising questions about where the original boundaries lay. The Supreme Court ruled that the changes made to Ellis Island during its use as an immigration station had resulted in primarily New Jersey's claim to the island, rather than New York's. Notably, in this ruling, the Court found the terms of the 1834 agreement to be critical in establishing the current jurisdictional makeup.

This resolution marked a significant moment in the long-standing competition and collaboration between the two states over shared resources and landmark sites. The decision was not just about geographical boundaries but also impacted issues such as tourism, historical recognition, and state pride in relation to Ellis Island's storied past. Ellis Island remains an iconic symbol of immigration and American opportunity, and the ruling emphasized its connection to New Jersey history.