If you have ever tried to understand how sanctuary cities actually work under federal law, the short answer is this: state and local governments choose not to use their own officers, jails, and databases to help Immigration and Customs Enforcement carry out civil immigration arrests. Federal law still applies everywhere. Local police just decline to do the federal government’s paperwork for it.
The mechanics get more interesting once you peel back the political slogans. Sanctuary policies sit on top of three constitutional principles: the Tenth Amendment’s reservation of powers to the states, the Supremacy Clause’s preemption of conflicting state law, and the anti-commandeering doctrine the Supreme Court has built around them. When a mayor declares a city a sanctuary, they are not declaring independence from Washington. They are drawing a line between what the federal government can do directly and what it can force local governments to do on its behalf.
I have spent the last few weeks reading congressional research, federal court rulings, and city ordinances to put this guide together. I have also compared how different states implement their own versions of sanctuary rules, from California’s broad TRUST and Values Acts to narrower county-level policies in the Midwest. Below is a plain-English breakdown of what sanctuary cities do, the legal architecture that lets them do it, the policies they pass, and where the active legal fights stand in 2026. If you have ever felt like the public conversation skipped over the actual mechanics, this guide is meant to fill that gap.
Table of Contents
What a sanctuary city actually is
A sanctuary city is a state, county, or municipal jurisdiction that limits its cooperation with federal immigration enforcement. The term has no single legal definition. There is no federal statute that uses the words “sanctuary city,” no official federal list of them, and no federal designation process. Cities, counties, and states adopted the label themselves, beginning in the 1980s, to signal that local police would not act as de facto immigration agents.
The label covers a wide spectrum. At one end are jurisdictions that refuse to honor Immigration and Customs Enforcement (ICE) civil detainers and refuse to share citizenship data with federal databases. At the other end are jurisdictions that pass statutes banning nearly all forms of cooperation, including voluntary cooperation. Most jurisdictions sit somewhere in the middle, with rules that require judicial warrants before any cooperation is allowed.
Estimates of how many sanctuary jurisdictions exist in the United States vary widely. Some counts include only cities that have passed formal ordinances. Others include counties, townships, and entire states whose laws restrict cooperation. The number fluctuates whenever a new law passes or a court ruling forces a jurisdiction to revise its policy. As of 2026, the rough range cited by most research groups runs from several hundred cities to over a thousand jurisdictions, depending on how the term is defined.
Here is the part that often gets lost in political debate. Sanctuary jurisdictions do not block federal immigration enforcement. ICE officers can still operate anywhere in the country. Federal agents can still make arrests, serve warrants, and conduct removals. What sanctuary policies limit is local help. They keep state and local officers from being pulled into a federal civil enforcement system.
This distinction is the heart of how sanctuary cities work under federal law. Federal authority is intact. Local participation in that authority is what the policy touches. The local government is essentially saying: we will not spend our budget, our officers, or our jail space on your civil cases.
How sanctuary cities work under federal law
To understand how sanctuary cities actually work under federal law, you have to understand how federal immigration enforcement is structured. Federal immigration law is enforced almost entirely by federal officers, but historically ICE has relied heavily on local jails to hold suspected noncitizens past their release date. That cooperation is voluntary at the local level. Sanctuary policies take it off the table.
Most sanctuary policies touch four practical areas. First, they limit compliance with ICE detainers. A detainer is a request, not a warrant. ICE asks a local jail to hold a person an extra 48 hours so federal agents can pick them up. Sanctuary jurisdictions either ignore the request or honor it only when ICE presents a judicial warrant signed by a judge. The practical effect is that people who would have been picked up at the jailhouse door are released instead.
Second, they restrict information sharing. Officers may be prohibited from telling ICE about a person’s release date, home address, or court schedule. Some sanctuary jurisdictions also restrict the use of federal immigration databases during routine policing. The idea is to keep local law enforcement databases from becoming recruitment tools for ICE.
Third, they bar local officers from stopping, detaining, or arresting a person based solely on suspected immigration status. This is the rule that prevents a traffic stop from turning into a deportation. Officers can still investigate crimes, make arrests, and run identification checks. They just cannot add immigration status to the list of triggers for state action.
Fourth, they limit participation in federal immigration programs. The main one is 287(g), which lets local officers perform immigration functions under ICE supervision. Sanctuary jurisdictions typically decline to sign 287(g) agreements. Some also decline to participate in the Priority Enforcement Program, the Secure Communities program, and similar federal-local partnerships.
The federal government can still enforce immigration law directly in any of these places. What changes is whether the local police act as a force multiplier for ICE. In practical terms, sanctuary policies make civil immigration enforcement harder, slower, and more resource-intensive for federal agents. They do not stop it.
One often overlooked detail is that sanctuary policies do not require officers to lie to ICE or actively interfere with federal operations. There is no requirement to mislead federal agents or destroy records. The policy is one of non-cooperation, not obstruction. The line between the two is what most of the active lawsuits turn on.
The constitutional and legal foundation
The legal foundation for sanctuary policies rests on three doctrines that often get confused. The Tenth Amendment reserves powers not delegated to the federal government to the states or the people. The Supremacy Clause says federal law preempts conflicting state law. The anti-commandeering doctrine, drawn from Supreme Court cases, says the federal government cannot order state or local officials to administer federal programs.
These doctrines can pull in opposite directions. Congress has broad power over immigration under the naturalization clause. But the federal government cannot conscript state officers to carry out that power. The Supreme Court settled the conscription point in New York v. United States (1992) and Printz v. United States (1997). Those rulings struck down federal laws that required state or local officers to perform background checks or enforce federal regulations.
Printz is the case that sanctuary advocates lean on most heavily. It held that “the federal government may neither issue directives requiring the States to address particular problems, nor command the States’ officers, or those of their political subdivisions, to administer or enforce a federal regulatory program.” That sentence is the legal backbone of the sanctuary movement.
Federal preemption still matters. If Congress passes a law directly regulating immigration, and the law is constitutional, it preempts any state law that conflicts with it. Sanctuary policies are constitutional because they refuse to act, not because they pass a conflicting statute. The Supreme Court has never held that jurisdictions must participate in federal immigration enforcement. That silence is what sanctuary advocates call permission.
The interplay between Section 1373 and sanctuary policies is a good example. Section 1373 prohibits state and local governments from restricting their officials from sending citizenship information to federal authorities. Sanctuary jurisdictions comply with Section 1373 by not restricting their officers from sharing information, even if they do not actively gather or transmit that information themselves. Federal courts have generally agreed with that interpretation, although the executive branch has tried to read the statute more aggressively.
Another foundational case is Arizona v. United States (2012). The Supreme Court struck down several Arizona immigration provisions as preempted by federal law, but it also acknowledged that the federal government could not force Arizona to actively enforce federal immigration priorities. The decision was a partial win for both sides and remains the most cited modern ruling on the overlap between state and federal immigration authority.
Types of sanctuary policies in practice
Sanctuary policies come in several recognizable flavors, and the names matter. A “detainer non-compliance” ordinance tells local police to ignore ICE detainer requests unless ICE shows up with a judicial warrant. A “don’t ask” policy prohibits officers from inquiring about a person’s immigration status during routine policing. An “information sharing” restriction bars the city from telling federal agents when someone will be released from custody.
Some jurisdictions pass “private” or “ID-only” policies that bar officers from honoring immigration detainer requests unless the person presents a valid local identification. That rule usually shows up after a settlement in which a U.S. citizen was detained based on an ICE request. The legal theory is that officers may not hold someone based on a non-judicial request from a federal agency. Several large cities adopted ID-only rules after high-profile wrongful detentions.
Then there are state-level sanctuary laws. California, for example, has passed statutes restricting cooperation with federal immigration enforcement through multiple legislative sessions. The Values Act limits the use of local resources for immigration enforcement. The TRUST Act limits compliance with ICE detainers. Other states have adopted narrower rules. Oregon, Washington, and New York have similar frameworks. The key difference between a state sanctuary law and a city ordinance is reach. A state law covers every county and municipality inside it unless the state legislature carves them out. A city ordinance covers only the city.
Finally, some jurisdictions pass “values” resolutions that have no enforcement mechanism. These are political statements, not operating policies. They tend to show up in smaller towns and counties. Whether they matter in court depends on whether the resolution is interpreted as binding local officials. Courts have generally treated resolutions as expressions of policy, not as enforceable directives.
Each type of policy is enforced differently. Detainer policies are easy to track because the data is recorded in jail management systems. Information sharing policies depend on officer training and audit. Don’t-ask policies are harder to monitor because they happen during individual interactions. State laws generally come with stronger enforcement mechanisms than city ordinances.
Public safety impact and crime data
The question most people actually want answered is whether sanctuary policies make communities safer or more dangerous. Peer-reviewed research has consistently found that sanctuary policies do not increase crime rates. Some studies have found a measurable decrease in certain categories of crime, particularly among Latino populations.
The mechanism researchers point to is community trust. When undocumented residents believe local police will hand them over to ICE, they stop reporting crimes, stop cooperating as witnesses, and stop calling for help during domestic violence incidents. Sanctuary policies are designed to reverse that dynamic. The goal is to keep local policing focused on local safety, not on federal civil enforcement.
There is also an economic dimension. Studies of sanctuary jurisdictions have found modest positive effects on wages and employment for native-born workers in some industries, though the effects vary. The economic argument cuts both ways. Opponents point to the cost of providing services to undocumented residents. Supporters point to the tax revenue generated and the labor force contribution.
What is not in dispute is that sanctuary policies are correlated with higher reporting of certain crimes. Studies of California’s TRUST Act and similar policies have documented an uptick in reporting among immigrant communities. Critics dispute the methodology. Supporters cite it as evidence the policies work as intended. Most mainstream criminologists agree that sanctuary policies do not increase violent crime rates.
Local data from major sanctuary cities in 2026 shows continued declines in overall crime compared to historical baselines. Some categories, like homicide and robbery, have seen modest increases since the pandemic, but those trends appear in non-sanctuary cities as well. Researchers generally attribute the post-pandemic spikes to broader social factors rather than to immigration policy.
The trust-building argument is harder to measure but consistently surfaces in surveys of immigrant residents. People who believe local police will not report them to ICE are more willing to file reports, serve as witnesses, and cooperate with investigations. That cooperation improves clearance rates for serious crimes. The full effect is hard to quantify, but it is part of why many law enforcement leaders in sanctuary jurisdictions support the policies.
What sanctuary cities do not do
Most public confusion about sanctuary cities comes from a list of things they do not actually do. Sanctuary cities do not prevent ICE from making arrests inside their boundaries. ICE agents can walk into any public space in any city and make an arrest. Sanctuary policies restrict local cooperation, not federal action.
Sanctuary cities do not shield noncitizens from criminal prosecution. State and local prosecutors pursue criminal cases the same way they always have. A noncitizen who commits a violent crime is prosecuted under state criminal law. Federal immigration consequences may follow, but those happen inside the federal system.
Sanctuary cities do not give noncitizens a right to remain in the country. They do not provide amnesty. They do not override federal removal orders. A person with a final order of removal can still be removed by ICE, regardless of the local jurisdiction’s policies. Sanctuary policies affect whether local police help with the pickup. They do not affect whether ICE does the removal.
Sanctuary cities do not refuse to honor judicial warrants. Federal judges sign arrest warrants. Sanctuary jurisdictions honor those warrants the same as any other. The dispute is over administrative detainers, which are signed by ICE officers, not judges. The legal distinction matters because the Constitution treats judicial warrants and administrative requests very differently.
Sanctuary cities also do not bar cooperation with federal law enforcement on non-immigration matters. Local police still share fingerprints, run background checks, and exchange information with FBI, DEA, and ATF for criminal investigations. Sanctuary policies are narrow by design. They target one specific area of federal activity. They leave everything else intact.
Finally, sanctuary policies do not require officers to actively mislead federal agents. Officers can respond truthfully to ICE inquiries. They just cannot volunteer information beyond what is required by law. The line is between non-cooperation and obstruction, and sanctuary policies are written to stay on the non-cooperation side of it.
Federal challenges and 2025-2026 legal battles
The legal landscape around sanctuary cities has shifted sharply since the start of 2026. Executive orders in the first months of the new administration have attempted to condition federal grant money on broader cooperation with ICE. Several cities and states have sued. The federal government has argued that conditions on Byrne JAG and similar grants are lawful exercises of congressional spending power. Sanctuary jurisdictions have argued the conditions cross into unconstitutional commandeering.
Courts have split. Some federal district courts have issued preliminary injunctions blocking the grant conditions. Appeals courts have begun weighing in. The Supreme Court has not yet taken a sanctuary-specific case this term, but the underlying constitutional question is live. The administration has also explored criminal charges against local officials under theories of obstruction and harboring, though most legal scholars view those theories as inconsistent with Printz.
One active fight involves Section 1373 of the Immigration and Nationality Act. That statute bars state and local governments from restricting their officials from sharing citizenship information with federal authorities. Sanctuary advocates argue the statute is a toothless information sharing rule because it does not require jurisdictions to share information. Federal courts have largely agreed. Congress is now debating amendments to clarify whether Section 1373 is mandatory or permissive.
Another fight involves state-level laws that criminalize harboring. Sanctuary opponents have tried to use those statutes against local officials who refuse to cooperate with ICE. Prosecutors have generally been unwilling to bring such charges because the elements are hard to meet. Knowingly harboring a fugitive is a specific intent crime. A mayor who refuses to use city resources for civil immigration enforcement is not harboring anyone.
What has emerged is a steady stream of court rulings, settlements, and political confrontations, but no clean resolution. The legal structure is stable because it tracks constitutional principles the Supreme Court has settled. The political fights are unstable because they touch immigration, federalism, and public safety at the same time.
In the states, the response has varied. Some governors have signed executive orders banning sanctuary policies. Other states have passed laws shielding local governments from federal pressure. The result is a patchwork where a person in one state can face very different treatment based solely on which side of a state line they live on. Federalism produces this kind of variation. The Supremacy Clause and the Tenth Amendment both leave room for it.
One trend worth watching is the rise of private right of action statutes. Several states have passed laws that allow individuals to sue local governments for harms caused by sanctuary policies. These statutes have generally been struck down or narrowed by federal courts, but they represent an emerging legal theory that could reshape the debate in 2026 and beyond.
There is also the question of state preemption. State legislatures in some jurisdictions have passed laws that prohibit cities from adopting sanctuary policies. Those state preemption laws have been challenged in court under theories of local authority and home rule. The outcomes have varied, and the Supreme Court has not stepped in to resolve the split. Expect more litigation in this area.
Looking ahead, expect three things to drive the conversation through the rest of 2026. First, the grant condition cases will continue to move through the federal courts, and at least one will likely reach the Supreme Court within the next year. Second, Congress may attempt to amend Section 1373 or pass new statutes that narrow the anti-commandeering doctrine in the immigration context. Third, state legislatures will continue to use sanctuary policy as a political flashpoint, with bills introduced in both directions in nearly every legislative session.
The policy debate is unlikely to settle any time soon. The constitutional framework gives both sides room to maneuver. Federal courts will continue to referee the boundary. State and local governments will continue to push against that boundary in both directions. The only certainty is that the legal question will keep producing court rulings, executive orders, and political confrontations for years to come.
Frequently asked questions
Do sanctuary cities receive money from the federal government?
Yes. Sanctuary jurisdictions receive federal funds through standard programs like Byrne JAG grants, FEMA assistance, transportation funding, and Medicaid reimbursements. Sanctuary status does not disqualify a city from federal funding, although the federal government has tried in 2026 to condition certain grants on broader cooperation with ICE. Courts have issued mixed rulings on those conditions.
Does the constitution say anything about sanctuary cities?
The Constitution does not mention sanctuary cities directly. The legal authority for sanctuary policies comes from the Tenth Amendment, which reserves non-federal powers to the states, and the anti-commandeering doctrine from cases like Printz v. United States. The Supremacy Clause gives Congress broad authority over immigration, but the Supreme Court has ruled that federal authority does not include the power to force state and local officers to enforce federal law.
Has the Supreme Court ruled on sanctuary cities?
The Supreme Court has not issued a direct ruling on sanctuary city policies. It has, however, ruled on the underlying constitutional principle in cases like New York v. United States and Printz v. United States, holding that the federal government cannot compel state or local officials to administer federal programs. Sanctuary advocates treat those rulings as the controlling framework.
Do sanctuary cities violate federal law?
No. There is no federal statute that requires state or local jurisdictions to cooperate with civil immigration enforcement. Sanctuary policies are based on the absence of a federal mandate, not a defiance of one. Federal courts have generally held that jurisdictions may decline to participate in federal immigration enforcement without violating federal law.
Can sanctuary city officials be prosecuted?
Prosecutions against local officials for declining to cooperate with ICE have been rare. The federal harboring statute requires specific intent to help someone evade detection, and courts have held that non-cooperation is not the same as harboring. Most legal scholars view such prosecutions as inconsistent with the anti-commandeering doctrine established in Printz v. United States.
The bottom line on how sanctuary cities actually work under federal law
Sanctuary policies are not loopholes. They are a structured refusal to use local resources for federal civil enforcement, anchored in Tenth Amendment and anti-commandeering case law. Federal immigration authority remains intact in every jurisdiction. What changes is whether state and local governments spend their own officers’ time on it.
As 2026 progresses, expect the legal battles to keep moving through federal courts. Expect new executive orders and new state laws. Expect the political heat to stay high. The constitutional framework, however, will keep sanctuary policies legal until the Supreme Court says otherwise.