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Fact check: Which countries have the highest number of immigrants crossing the US border illegally?
Executive Summary
The best-supported public data show that Mexico has long been the largest single country of origin for unauthorized immigrants in the United States, but recent analyses document a clear shift toward Central and South American origin countries in the population of more recent arrivals. Available reports and statements through mid‑2025 emphasize declining overall unlawful border encounters while noting that origin-country detail is patchy in publicly released monthly enforcement summaries, so definitive, up‑to‑the‑month rankings of “who is crossing illegally now” are not consistently published [1] [2] [3].
1. What advocates and analysts have claimed loudly — and what the data actually say
Multiple sources claim that migrants from Mexico once dominated the unauthorized population and that more recent flows increasingly originate in Central and South America, a claim supported by demographic analyses showing a decline in Mexico’s share among recent arrivals to about 19% for those arriving within the past ten years [2]. The Migration Policy Institute estimated that, as of 2021, Mexico, Guatemala, Honduras, and Venezuela were leading origins among unauthorized immigrants overall and that migrants from Latin America and the Caribbean made up 79% of the unauthorized population, which is consistent with longstanding migration patterns [1]. These figures provide the strongest basis for saying Mexico remains large historically but that Central and South American countries now supply a growing share.
2. Enforcement numbers say crossings have dropped — but they don’t show origin detail
Border Patrol and Department of Homeland Security updates cited dramatic drops in monthly encounters in mid‑2025, including a 93% year‑over‑year decline in May encounters reported by CBP and monthly arrest declines noted by the White House and news outlets, pointing to just over 6,000 apprehensions in June in one report [3] [4] [5]. These enforcement summaries emphasize volume trends, not comprehensive origin breakdowns. That gap means headline counts of “illegal crossings” do not automatically translate into reliable country‑by‑country rankings without additional nationality reporting that is inconsistently released in monthly operational updates.
3. Think‑tank analysis documents a substantive origin shift in recent years
A February 2025 analysis quantified a compositional change: fewer recent undocumented arrivals are from Mexico and larger shares now come from Central and South America, reflecting migration drivers, asylum patterns, and enforcement changes [2]. This analysis gives a temporal nuance: while the long‑term unauthorized population retains many Mexican nationals, the cohort of more recent arrivals has diversified. Policy and media debates often blur the distinction between the stock of unauthorized residents (longstanding population) and the flow of recent crossers, creating confusion about which countries “have the highest numbers” depending on whether one examines cumulative population or recent quarterly/annual flows.
4. Government claims about removals and departures complicate interpretation
Government statements claiming large numbers of removals or departures — for example, assertions about more than 2 million removals or 1.6 million self‑deportations within a specific enforcement window — are contested and not accompanied by consistent origin breakdowns in the cited briefings [6] [7]. News analyses note methodological limits in estimating unauthorized population decline and emphasize that departure tallies do not directly identify current origin patterns among those still attempting to cross, which leaves the public debate over “which countries are sending the most” only partially addressed by removal statistics [7].
5. Major data gaps: why precise current rankings are elusive
Publicly accessible CBP monthly updates and many policy briefings focus on encounter totals and aggregate trends, not on a standardized, regularly published list of top origin countries for apprehensions [3] [5]. Migration research organizations provide periodic snapshots of the unauthorized population by origin but lag real‑time flows; therefore, claims about “highest numbers crossing now” often outpace the data that would substantiate them. The methodological mismatch — stock versus flow, annual surveys versus operational counts — is the central reason for persistent uncertainty.
6. Competing narratives and potential agendas behind the claims
Think tanks and research groups emphasize demographic shifts to inform policy debate and often frame Mexico’s declining share as evidence of policy effects or changing migration drivers [1] [2]. Government releases highlighting large drops in encounters or large numbers of removals tend to stress enforcement success without providing origin detail, which can serve an enforcement‑oriented narrative [3] [4] [6]. Media accounts vary between amplifying enforcement milestones and highlighting humanitarian or structural causes, so readers should treat each claim as serving differing interpretive goals [5] [7].
7. Bottom line — what can be responsibly stated today
Historical and peer‑reviewed migration estimates show Mexico as the largest single country of origin historically, while more recent arrival cohorts increasingly come from Central American and South American countries such as Guatemala, Honduras, and Venezuela [1] [2]. Current CBP monthly enforcement releases through mid‑2025 document sharp declines in encounters but do not consistently publish country‑by‑country origin rankings, so any definitive, up‑to‑the‑month list of “highest‑number origin countries for illegal crossings” cannot be fully verified from the available public summaries [3] [5].