In the months following Trump’s 2016 election as U.S. president, scores of cities across the United States instituted or reaffirmed “sanctuary” measures that impede federal immigration enforcement actions in their midst. Yet in the heart of these “sanctuary” cities, many immigrants remain vulnerable to deportation. This article describes one community campaign to identify, track, and stop a mechanism through which urban immigrants are detained and deported: data sharing between local police agencies and federal immigration officials. We draw on Kyle Walker’s (2015) framework of place, scale, and networks of local immigration politics to show how overlapping scales of immigrant policing ultimately jeopardized Chicago’s promise to be a place of immigrant sanctuary. We then describe how community organizers exploited this tension as they exposed the effects of Chicago police data sharing practices on black and Latinx Chicagoans and campaigned for a stronger city sanctuary policy.