Between 1921 and 1939, the border separating Detroit, Michigan, from Windsor, Canada, represented a key site for undocumented immigration on America’s northern border, and the migrants in question were European. This essay examines industrial urban America in the wake of 1921 and 1924 Immigration Acts to reveal the effects of restriction and policing on America’s emerging welfare state. It finds that in Detroit, after federal policies gave nativism the force of the law, local smuggling, policing, and enforcement practices branded foreign-born Europeans as illegal regardless of their legal status. During the New Deal Era, when the federal government built America’s welfare system, the stakes for belonging to the nation-state became higher than ever. In this moment of transition, local actors drew on rhetoric connecting foreigners to crime and dependence to urge federal policymakers to tie welfare benefits to citizenship. These local initiatives in Detroit and across the nation prompted the federal government to purge non-citizens from the Works Progress Administration, the new welfare program most associated with dependence and relief. Ultimately, this essay argues that a shift in national mood about foreignness in urban America took hold of the United States in the 1920s and shaped federal welfare policy by the 1930s.