SafelyArrived - US Border Crossing - Guides - FAQs - Checklists - 42

100 Mile Border Zone and the 4th Amendment

What It Is

The 100-mile border enforcement zone is a legal designation that grants U.S. Customs and Border Protection (CBP) and Border Patrol agents certain authorities within 100 air miles of any U.S. land or coastal border. This zone is a significant legal concept because it modifies the standard Fourth Amendment protections against searches and seizures that apply in the rest of the country. the legal authority was granted by a law passed in 1946, but the specific 100-mile distance was administratively defined in a regulation that stemmed from the 1952 Act.

Legal Foundation

In 1946, Congress quietly passed a statute giving U.S. Customs and Border Protection the authority to stop and search all vehicles within a “reasonable distance” from the border. This initial law provided the legal basis for the enforcement zone but did not specify the exact distance.  In the 1952/1953 Regulation, the phrase “reasonable distance” was later defined by federal regulations. The key regulation, 8 C.F.R. § 287.1, was enacted under the authority of the Immigration and Nationality Act of 1952. This regulation officially set the distance at 100 air miles from any external U.S. boundary.  The federal government defines a “reasonable distance” as 100 air miles from any external boundary (all land borders and coastlines) of the U.S.  This includes not just land borders with Mexico and Canada, but also the entire U.S. coastline, meaning both ocean and Great Lakes coastlines count as “external boundaries.”  U.S. immigration law (8 U.S.C. § 1357) allows U.S. Border Patrol to operate within a “reasonable distance” from the external boundary of the U.S. The Department of Justice defined reasonable distance in regulation (8 C.F.R. § 287.1) as 100 air miles from any U.S. land or coastal border.

Geographic Scope and Population Impact

The zone’s reach is massive:

  • Two-thirds of the U.S. population, or about 200 million people, reside within this expanded border region, according to the 2010 census.
  • Most of the 10 largest cities in the U.S., such as New York City, Los Angeles, and Chicago, fall in this region.
  • Some states, like Florida, lie entirely within this border band so their entire populations are impacted.
  • Daily enforcement is concentrated in the Southwest border region and at fixed checkpoints, not everywhere inside the zone.

What CBP Can Do in the 100-Mile Zone

  • Border Patrol has the authority to stop and question people about their citizenship/immigration status inside this zone.

  • They may also board and search vehicles, vessels, and aircraft without a warrant, but this power is not unlimited — they must have a valid immigration enforcement purpose.

  • Checkpoints (common in AZ, NM, TX, CA) are used to briefly ask about citizenship and visually inspect vehicles.

  • Beyond that, extended detention, vehicle searches, or device searches usually require consent, probable cause, or a warrant (though how this plays out can vary).

Enhanced Authority:

  • CBP claims authority to board a bus or train without a warrant anywhere within this 100-mile zone 
  • CBP boards buses and trains in the 100-mile border region either at the station or while the bus is on its journey
  • CBP operates immigration checkpoints along the interior of the United States at both major roads — permanent checkpoints — and secondary roads — “tactical checkpoints”

Limited Jurisdiction:

  • As a general matter, these agents’ jurisdiction extends only to immigration violations and federal crimes 
  • Border Patrol, nevertheless, cannot pull anyone over without “reasonable suspicion” of an immigration violation or crime.

Interior Checkpoints

At these checkpoints, every motorist is stopped and asked about their immigration status. Agents do not need any suspicion to stop you and ask you questions at a lawful checkpoint, but their questions should be brief and related to verifying immigration status.

Border Patrol, according to news reports, operates approximately 170 interior checkpoints throughout the country.

Your Rights in the 100-Mile Zone

Constitutional Protections Still Apply: The Fourth Amendment of the U.S. Constitution protects people from random and arbitrary stops and searches even within this zone.

Right to Remain Silent: Although these situations are scary, and it may seem that CBP agents are giving you an order when they ask you questions, you are not required to answer and can simply say you do not wish to do so. As always, you have the right to remain silent.

Detention Requirements: If the agent wishes to actually detain you — in other words, you are not free to leave — the agent needs at least reasonable suspicion. The longer CBP detains you the more suspicion they need — eventually they will need probable cause once the detention goes from brief to prolonged .

Key Questions to Ask

If stopped by CBP agents:

  • “Am I free to leave?” or “Am I being detained?” 
  • If detained: Ask for their basis for reasonable suspicion or probable cause

Controversies and Concerns

Civil Rights Issues: In practice, Border Patrol agents routinely ignore or misunderstand the limits of their legal authority in the course of individual stops, resulting in violations of the constitutional rights of innocent people.

Accountability Problems: These problems are compounded by inadequate training for Border Patrol agents, a lack of oversight by CBP and the U.S. Department of Homeland Security, and the consistent failure of CBP to hold agents accountable for abuse.

“Constitution-Free Zone” Criticism: Border regions are often treated as zones of exception for human rights and civil rights, laying the foundation for abuse not just along our nation’s borders but across the country.

Common Misunderstandings

What It’s NOT:

  • It’s not a “constitution-free zone” – constitutional rights still apply
  • CBP cannot conduct unlimited searches – they still need reasonable suspicion for most activities
  • It doesn’t give CBP the same powers as at actual border crossings

What It IS:

  • An area where CBP has additional authorities beyond normal law enforcement
  • A zone where interior immigration checkpoints can operate
  • An area where CBP can board public transportation without warrants

Legislative Efforts

In the last Congress, Senator Kirsten Gillibrand (D-NY) introduced the DATA Act, which would require documentation for stops that exceed “a brief and limited inquiry”, showing ongoing congressional concern about these expanded powers.

The 100-mile zone represents a significant expansion of federal law enforcement authority that affects the majority of Americans, often without their knowledge. While constitutional rights still apply, CBP has enhanced powers in this zone that don’t exist elsewhere in the United States.

Conclusion

The 100-mile zone does not erase constitutional rights. The 4th Amendment (protection from unreasonable searches and seizures) still applies, but courts have allowed broader latitude for “brief stops and questioning” related to immigration in this area.