In this cutting-edge interpretation of the late nineteenth-century United States, Cameron Blevins argues that the US Post wove together two of the era's defining projects: western expansion and the growth of state power. Between the 1860s and the early 1900s, the western United States underwent a truly dramatic reorganization of people, land, capital, and resources. As millions of settlers moved into the region, they relied on letters and newspapers, magazines and pamphlets, petitions and money orders to stay connected to the wider world. Paper Trails maps the spread of the US Post using a dataset of more than 100,000 post offices, revealing a new picture of the federal government in the West. The western postal network bore little resemblance to the civil service bureaucracies typically associated with government institutions. Instead, the US Post grafted public mail service onto private businesses, contracting with stagecoach companies to carry the mail and paying local merchants to distribute letters from their stores. These arrangements allowed the US Post to rapidly spin out a vast and ephemeral web of postal infrastructure to thousands of distant places. The postal network's sprawling geography and localized operations forces a reconsideration of the American state, its history, and the ways in which it exercised power.