How does the Department of Homeland Security define and track illegal immigration in their 2024 reports?

Executive Summary — Short, Direct Answer to the Question

The Department of Homeland Security (DHS) treats “illegal immigration” in two related ways: as a population category—people present in the United States without legal authorization—and as a set of enforcement outcomes measured by operational actions such as apprehensions, encounters, removals, and returns. DHS’s 2024 outputs include population estimates labeled “illegal aliens” or “unauthorized immigrants” and enforcement tallies reported by component agencies (primarily CBP and ICE); these outputs use discrete metrics (encounters, arrests, removals, returns, detentions) rather than a single unified measure of who is “illegal” ^{[1] [2] [3]}. DHS publishes those population estimates and enforcement tables in its Yearbook and in component reports, while Congress and independent researchers present alternative definitions and estimates that sometimes differ in scope and method ^{[4] [5] [6]}.

1. How DHS Labels and Defines “Illegal” — The Language That Drives the Numbers

DHS defines people “not authorized to be in the country” to include those who entered without inspection and those who overstayed temporary admissions; the phrase “illegal alien” appears in some DHS products to denote this group ^[1]. That administrative definition is functionally narrow: it classifies status based on immigration authorization, not criminal culpability or permanence of residence. Independent organizations and oversight bodies use related terms—“unauthorized immigrants,” “undocumented,” or “illegal presence”—and sometimes adopt different cutoffs or subcategories (e.g., recent entrants versus long-term overstays), so direct comparisons require care ^{[5] [6]}. The label matters because DHS numbers are anchored to authorization status and enforcement records, which capture different slices of the same phenomenon.

2. What DHS Tracks in 2024 Reports — Enforcement Actions Over Population Dynamics

DHS’s 2024 reporting emphasizes operational enforcement metrics: CBP reports encounters and apprehensions at and between ports of entry, and ICE reports arrests, detentions, and removals through Enforcement and Removal Operations (ERO) ^{[3] [7]}. The Yearbook of Immigration Statistics lays out tables on apprehensions, removals, returns, and other administrative actions that form the backbone of DHS’s tracking ^[4]. Those metrics are event-driven: they count interactions with the enforcement system rather than the full stock of unauthorized residents, so they are sensitive to operational tempo, policy changes, and border conditions. DHS’s public outputs therefore present a mixture of flow data (encounters per period) and stock estimates (population size estimates), which are not interchangeable.

3. Population Estimates Versus Enforcement Counts — Different Methods, Different Stories

DHS produces population estimates labeled “illegal alien population estimates,” while CBP and ICE produce event counts like encounters, arrests, and removals ^{[2] [3]}. External researchers such as Pew and Congressional Research Service provide alternative population estimates and methodological discussion but do not substitute for DHS’s operational statistics ^{[5] [6]}. The key methodological divide is that population estimates attempt to quantify the total stock of unauthorized residents—often using modeling or residual techniques—whereas DHS enforcement counts measure contacts with immigration authorities, and policy shifts (e.g., asylum processing changes, parole programs) can cause these two series to move in different directions.

4. What the 2024/Yearbook Data Showed — Volume, Trends, and Important Nuance

DHS’s 2024 Yearbook tables and CBP/ICE releases highlight high-volume enforcement activity: CBP reported millions of enforcement encounters for FY2024, split between Border Patrol and Office of Field Operations, and noted changes over the calendar year in monthly updates ^{[3] [8]}. ICE’s ERO statistics catalog interior arrests, detentions, and removals for the period and the Yearbook compiles removals and returns in annual tables ^{[7] [4]}. These numbers document system workload and enforcement outcomes but do not by themselves quantify the total unauthorized population or explain the drivers behind fluctuations—operational emphasis, policy changes, and seasonal migration patterns all shape the counts.

5. Multiple Viewpoints and What They Emphasize — Who’s Measuring What, and Why It Matters

Congressional and academic analyses stress the limits of enforcement data for population measurement and caution that DHS’s operational metrics can reflect policy and resourcing shifts as much as migration flows ^{[6] [5]}. DHS components emphasize operational accountability—how many encounters, arrests, removals—while researchers emphasize methodological transparency for population estimates ^{[7] [5]}. Stakeholders’ agendas matter: enforcement-focused authorities highlight declines or increases in encounters to show operational success or pressure, while researchers and advocates focus on estimation uncertainty and the human implications of different counting choices.

6. Bottom Line — How to Read DHS’s 2024 Outputs Responsibly

Treat DHS’s 2024 reports as two complementary but distinct outputs: event-driven enforcement statistics from CBP and ICE, and population estimates labeled “illegal aliens” produced for analytic use; neither alone answers every policy question ^{[1] [2] [3]}. For policy analysis, combine enforcement flows with independent population estimates and note the timing and methodological differences that drive divergences ^{[5] [6]}. When reporting or comparing figures, always specify whether the number is an enforcement encounter, a removal, a return, or a population estimate—those distinctions determine what the data can and cannot show.