“The Adjudicatory State” traces the collision between the federal legal vision for the early American West and the preexisting laws and customs that governed the region. To administer the vast region it obtained in the 1783 Treaty of Paris, the United States created the territorial system, under which federal officials would temporarily govern western “territories” until they achieved statehood. The federal government would also survey and sell the public domain to private purchasers. But these grand plans ran afoul of territorial realities. Both the Northwest Territory, encompassing much of the present-day Midwest, and the Southwest Territory, encompassing present-day Tennessee, were borderlands, places where Native peoples, French settlers, Anglo-American intruders, and land companies contended for sovereignty and property. Instead of crafting a new legal order, federal officials found themselves barraged with preexisting claims. The polyphony of claims played out especially clearly in the contests over land and so-called “Indian affairs.” In the territories, title derived from a complicated blend of Native, French, British, and state law. It fell to federal officials to understand and translate these plural rights of ownership into the single federal title that would undergird the federal land system. In Indian affairs, federal officials embraced a vision of federal sovereignty in which federal law would serve as the impartial arbiter in conflicts between Native nations and U.S. citizens. Yet early American law encompassed too much ambiguity and localism for centralized authority to succeed. Instead of relying on law, federal officials ultimately attempted to secure both peace and allegiance through liberal payments of federal funds to both Natives and U.S. citizens. The federal government’s role in the territories as an adjudicatory state adhered neither to an account that emphasizes federal power’s inexorable westward march nor to a straightforward narrative of federal failure against local customary practice. Through resolving claims, federal government slowly accreted authority, but in ways that defied classification as strong or weak. The process traced here also blurred the sharp dichotomy between informal and formal law, and suggests how the rise of federalism helped channel the plural claims of the borderlands into a framework of dual sovereignty.