by Jacob Kang-Brown, July 23, 2026

The federal system of incarceration and detention makes up a relatively small, but rapidly expanding, share of confinement in the United States. Between 1984 and 2026, the number of people confined by the federal government has exploded by 631%. And while that number is below its 2011 peak, federal incarceration and detention have grown by 12% in just the last two years.¹

The Trump administration’s recent, belligerent use of policing and prosecutions have already left their mark on the federal system, especially with regard to mass detention and deportation. But even so, it’s not easy to understand the scope of this corner of the system and how its practices and priorities have shifted over time. Opaque federal police and prison agencies make it hard to see these changes, or to know which agency is responsible. And it’s harder still to know what federal policy reforms or state and local resistance would be most effective to rein in runaway expansion plans.

In this briefing, we try to overcome these issues by piecing together data from various sources to provide a clearer picture of the patchwork federal system, from ICE detention and electronic monitoring to federal prisons and pretrial supervision. We show trends in detention and incarceration,² and examine the role that the criminalization of immigration (including the exploitation of a loophole in sanctuary policies) has played in shaping the system. Finally, we round out our analysis by spotlighting some of the glaring problems with federal pretrial detention and highlighting the fiscal costs of the system.

With a better grasp of the agencies involved and the mechanisms at play, people can work with their state and local governments to limit the reach of the federal system.

Today, 268,000 people are detained or incarcerated on federal authority, and 321,000 people face the threat of being locked up while under federal community supervision. Taken together, more than half a million people are under some kind of federal correctional control.³ But they are spread across four major agencies or authorities, depending on the charges and the status of their cases. For example, after a federal arrest, people are locked up in one of three primary ways:

1. Pretrial detention while a criminal case proceeds in federal court. They may be held without bail or, more often, unable to afford release on bail.
2. A sentence to incarceration. When someone takes a guilty plea or is convicted at (an exceedingly rare) trial, a judge can sentence them to incarceration.
3. ICE detention: They are confined while a civil case proceeds in immigration court or while awaiting deportation.

Additionally, many who aren’t locked up are instead under community supervision by either the federal criminal court system or ICE. In this section, we briefly explain which agencies are involved at various stages of the legal process and how they share resources to detain, incarcerate, and monitor so many people.

Pretrial detention. While being prosecuted in a federal criminal court, people are booked into custody of the U.S. Marshals Service (USMS or “the Marshals”). The Marshals provide space for pretrial detention to the federal courts, primarily via contracts with a network of local jails.⁴ While the Marshals’ role in criminalizing immigration is less visible, their detention network presents a loophole that allows the use of local resources for immigration enforcement despite “sanctuary” policies. It’s important to understand that the Marshals often serve the same purposes as ICE and share the same resources. Almost half of all people who face federal criminal charges in the course of the year are there for some kind of “criminal” violation of immigration law, such as returning to the United States after an earlier deportation.⁵ Meanwhile, ICE relies heavily on the Marshals’ network of local jails to detain people for civil immigration matters; only a small share of these individuals have criminal convictions.

Incarceration. After sentencing in a federal criminal court, people with short terms of incarceration are sometimes left in U.S. Marshals custody instead of being transferred to a federal prison. Many people don’t know that 1 in 5 people serving a federal sentence of incarceration on any given day are in USMS custody. The Federal Bureau of Prisons handles everyone else with sentences to incarceration, using its detention centers, penitentiaries, correctional institutions, and prison camps.

Immigration detention. In federal civil immigration cases, people are detained in ICE’s detention network. This network consists of detention centers operated by private prison companies, but also include some federal detention centers, state prisons, Bureau of Prisons facilities, and ICE offices. Importantly, ICE often has access to the USMS detention network of local jails as well, as intergovernmental service agreements commonly include both agencies.⁶ ICE can also contract directly with local jails.

Community supervision: pretrial, probation, post-release, and for ICE. Beyond federal detention and incarceration, 321,000 people face community supervision and surveillance by the federal government, both of which come with the inherent threat of confinement for any alleged violation. Community supervision for people accused or sentenced for federal crimes is overseen by the federal courts’ Probation and Pretrial Services. ICE surveils hundreds of thousands of people on an “alternatives to detention” electronic monitoring program.⁷

This table breaks down how many people are involved in various parts of the system now:⁸

The longer-run trends of federal detention and incarceration are similar to the overall expansion of mass incarceration through the 1980s and 1990s.¹⁰ Since then, the federal system has continued to add huge numbers of people in immigration detention, especially during the Trump administrations. That increase in immigration detention, combined with the failure of the federal government to keep pace with broader declines in criminal punishment at the state and local levels over the past six years, has led to an overall spike in federal confinement.

The number of people confined by federal agencies is more than six times greater in 2026 than it was in 1984, although it remains below its 2011 peak. Note that this chart does not include confinement by state or local criminal legal systems.

Moreover, Congress has already approved funding for ICE to expand detention capacity to 135,000, almost double the current level. If used, this would drive federal confinement to all-time highs. Extreme levels of ICE arrests — like the 10,000 people arrested in the last 5 days of June 2026, and 2,000 on the weekdays that followed — will assuredly lead to even more people held in ICE detention.

In addition to the well-documented expansion of ICE detention, federal prosecutors, the U.S. Marshals, and the Bureau of Prisons together have played an overlooked role in the expansion of confinement for immigration-related reasons, detaining and incarcerating people on criminal charges that had commonly been treated as civil matters in the past.¹¹

Federal criminal prosecution allows immigration arrests and detention even in places with sanctuary policies.¹² That’s because of a longstanding loophole: ICE and other federal agencies can refer people for federal prosecution on immigration-related “crimes” and thus hold them in contracted local jails in sanctuary cities, counties, and states. In doing so, the Trump administration is transforming what are normally civil immigration matters into more serious federal crimes. This expands the overall federal incarceration system. As we have explained, every county with a U.S. Marshals contract is effectively signed up for this part of the mass detention and deportation agenda, even if they have sanctuary policies on their books.

We estimate the federal Bureau of Prisons and U.S. Marshals detained or incarcerated roughly 25,000 people on an average day in fiscal year 2025 for immigration-related criminal charges, up 45% from around 17,300 people in 2024.¹³ Federal prosecutors have been filing more cases against people for immigration-related offenses, sending people into the federal criminal legal system. Almost 50,000 people were charged and booked into U.S. Marshals custody for an immigration-related offense in fiscal year 2025 alone. The Trump administration plans to take this even further.

The Trump Administration projects that it will book 250,000 people into jail in fiscal year 2027.¹⁴ There were fewer than 100,000 federal bookings in 2024.

The most dramatic part of this projection is the expected booking of almost 110,000 people on immigration-related criminal charges, followed by sharp increases in the catch-all “other charges” group. Historically speaking, bookings in the “other” category primarily have been for supervision violations, followed by property offenses.¹⁵

Notably, the Trump administration also plans a rapid increase in the number of people booked on federal drug charges, indicating a return to the failed policies of the “war on drugs.” This will only compound problems within the federal pretrial system: people facing federal drug charges tend to be detained pretrial for longer than others (7.5 months before sentencing), in part because they often face protracted plea negotiations to avoid harsh mandatory-minimum charges.¹⁶ Aggressively prosecuting drug-related crime will exacerbate the harmful impacts of pretrial detention in the federal system.

The United States still incarcerates and detains its residents far more than peer nations on a per capita basis, and changes at the federal level remain absolutely necessary — though not sufficient on their own — to end mass incarceration. Federal policymakers have direct control over criminal and immigration law, agency budgets, and appointment and confirmation of agency directors, federal prosecutors, and judges. Their influence can be seen in the outsized growth of the federal criminal legal and immigration detention system, especially in recent years, when immigration detention has spiked.

At the top of any policy agenda must be addressing the injustice of ICE and civil immigration enforcement with their bloated budgets and lack of transparency and accountability. But the criminalization of immigration by the federal criminal courts, as well as the ongoing “war on drugs,” also demand action. Currently, federal judges and prosecutors use the vast detention network set up by the U.S. Marshals Service to lock people up in hundreds of different local jails and private prisons for the purposes of punishing what have not always been criminal offenses. Advocates and elected officials have fought back by ending law enforcement and jail collaborations with ICE. But policymakers need to go further and also block collaboration with other federal detention agencies like the U.S. Marshals. While federal policy action is essential to changing this system and reversing its buildup, states and local governments can take steps to limit it now.