The United States operates the world’s largest immigration detention system. On any given day, it can have upwards of 50,000 non-citizens in detention, even though detainee numbers fell dramatically after the onset of the COVID-19 pandemic. The annual numbers of unaccompanied children in custody also skyrocketed over the last decade, rising from just over 10,000 in the early 2010s to nearly 70,000 by 2019. The budget for operating the U.S. immigration enforcement system is astronomical: In 2016, the combined budget of enforcement agencies was $19 billion. The country’s sprawling detention estate includes beds in some 200 facilities, including privately operated detention facilities, local jails, juvenile detention centres, field offices, and “family residential centres.” The country has also supported the detention of migrants and asylum seekers in neighbouring countries and was a pioneer in offshoring detention.