Which U.S.-Mexico border sectors have the highest rates of illegal crossings and how do those statistics map to recent wall construction?
Executive summary
Tucson (Arizona) and Del Rio (Texas) were the busiest U.S.–Mexico border sectors for detected illegal crossings in late 2023 and into 2024, with Tucson repeatedly reported as the single busiest corridor and Del Rio often second in apprehension counts [1] [2]. Federal statements and administration fact sheets credit recent border-wall construction and other enforcement measures with sharp declines in overall encounters by late 2024–2025, but the public reporting provided does not supply a clear sector-by-sector map linking where new wall was built to the specific declines in individual sectors [3] [4].
1. Which sectors have the highest rates of illegal crossings — the raw picture
Multiple official and journalistic compilations show that Border Patrol’s Tucson sector recorded the largest number of apprehensions among the nine southwest sectors during the 2023–2024 surge (Tucson tally cited at 463,567 in a sector compilation and 80,185 arrests cited for December alone), with Del Rio frequently reported as the second-busiest sector in that same period [2] [1]. Public CBP encounter datasets aggregate encounters by sector and confirm that crossings are concentrated unevenly across the nine Border Patrol sectors that divide the nearly 2,000-mile border, a pattern reiterated in federal reporting and third‑party trackers [5] [6] [7].
2. Trends over time — surge, then decline
After a spike that peaked in late 2023 (December 2023 cited as a peak month in several compilations), reported encounters trended down through 2024 and into 2025, with federal briefings and independent outlets documenting sharp reductions in many sectors by late 2024 and into FY2026 preliminary months [5] [3] [8]. News analyses attribute that downward movement to a mix of policy changes, bilateral Mexican enforcement, and operational shifts at CBP; Axios specifically notes Mexico’s ramped-up enforcement as a material factor in the 2024 decline [9].
3. Wall construction claims and official framing
The Biden and subsequent Trump administrations’ public materials and press releases link border security gains to enforcement measures and, in the case of the Trump administration, a restart and expansion of physical wall construction; the White House and DHS statements assert that construction resumed and that encounters fell substantially after policy actions and construction efforts [4] [3]. DHS fact sheets report broad decreases in southwest‑border encounters between May and December 2024 and tout construction among other steps as part of a package of measures [3].
4. Where the evidence falls short — mapping crossings to new wall segments
The available reporting does not provide a comprehensive, sector-by-sector overlay that ties recent miles of new or refurbished wall directly to measured declines in that same sector; government encounter dashboards publish crossings by sector, and administration statements summarize construction activity, but public sources in this collection do not include a detailed geospatial reconciliation showing how many miles of new barrier were built in Tucson versus Del Rio, El Paso, Yuma, San Diego, or other sectors, nor a causal analysis attributing sector declines to specific wall segments [6] [7] [3] [4]. Any direct causal claim that “wall X in sector Y caused Z percent decline in crossings” is therefore beyond what these sources document.
5. Competing interpretations and implicit agendas
Political and institutional actors use the same datasets to support competing narratives: DHS and White House communications emphasize construction and enforcement to claim success in reducing encounters [3] [4], while independent analysts and rights groups highlight persistent humanitarian concerns, sector-level human costs (e.g., migrant recoveries noted by reporting) and the role of Mexican policy and other non‑barrier measures in driving trends [2] [1]. This divergence matters because emphasizing construction alone can obscure other drivers of migration flows and because the reporting here lacks the granular construction-to-sector correlation that would let observers validate either causal story fully [9] [2].
6. Bottom line
Tucson and Del Rio emerged as the two highest-volume southwest sectors during the surge period documented through late 2023 and into 2024, and federal officials later reported broad declines in encounters after policy changes and resumed wall construction; however, the supplied sources do not provide the detailed, sector-level mapping required to attribute those declines directly and exclusively to recent wall construction in specific sectors [1] [2] [3] [4]. Any firm causal linkage between discrete wall segments and sector‑level declines remains unproven in the reporting provided.