Today, U.S. Immigration & Customs Enforcement (ICE) detains a n average of 37,000 migrants each night. To do so, they rely on, and pay for, the use of hundreds of local jails. But this is nothing new; the federal government has been detaining migrants in city and county jails for more than 100 years. In The Migrant's Jail, Brianna Nofil examines a century of political, ideological, and economic exchange between the U.S Immigration bureaucracy and the criminal justice system gave rise to the world's largest system of migrant incarceration. Migrant detention is not simply an outgrowth of mass incarceration; rather, it has propelled carceral state-building and fostered intergovernmental policing efforts since the turn of the twentieth century.