Migrants with precarious immigration status in Canada encounter surveillant assemblages of illegalization that threaten their safety and ability to access social goods. Drawing on qualitative interviews, media stories, and government documents, this article analyses how surveillance is produced through various ways of knowing, by various actors, and in different institutions in Canada. My case study demonstrates that the sites of operation for surveillant assemblages of illegalization extend beyond immigration authorities and into more diffuse sources including the police, the health‐care sector, banks, employment agencies, and acquaintances. I also suggest that there is a level of overlap and integration among such sites, including the use of shared databases and the possibility that any interaction with precarious status migrants can be reported to immigration authorities.