How many illegal aliens entered USA between 2001 and 2008
Executive summary
Available federal and academic estimates do not provide a single exact tally of undocumented entries for the narrow span 2001–2008, but the weight of published reporting shows that most unauthorized migration peaked around 1999–2001 and then fell sharply through the 2000s; the Department of Homeland Security–based estimates summarized by analysts put roughly 3.9 million arrivals across the entire decade of the 2000s (2000–2009), which implies the 2001–2008 window is somewhat smaller but not precisely enumerated in the cited sources [1] [2].
1. What the major estimates say about arrivals in the 2000s
Government and academic work converge on the broad pattern: annual unauthorized arrivals were above one million around 1999–2001 and then dropped substantially through the rest of the decade, with cumulative arrivals across the 2000s (the decade 2000–2009) estimated at about 3.9 million according to a DHS-based summary used by the American Immigration Council and the Office of Homeland Security Statistics [1] [2].
2. Why a precise 2001–2008 count is not available in these sources
The chief public estimates (DHS/OIS, Pew, CMS and academic reconstructions) present either annual series that begin or peak near 1999–2001 or decadal period-of-entry tallies (e.g., “arrived in the 2000s”), but none of the provided snippets gives a direct tabulation labeled exactly “number who entered between 2001 and 2008,” so a precise published sum for that exact span cannot be confidently extracted from the available documents [1] [2] [3].
3. How to convert the available decade estimate into an approximate 2001–2008 figure
Using the decade total of roughly 3.9 million arrivals for the 2000s (2000–2009) as a starting point [2], and combining that with the documented pattern of very high arrivals in 2000–2001 followed by rapid decline (more than one million per year through 1999–2001 and falling afterward) [1], the 2001–2008 subset is plausibly lower than 3.9 million — likely on the order of a few million — but the precise number depends on year-by-year counts not reproduced in the provided excerpts [1] [2].
4. What academic reconstructions add and their limits
Academic analyses that reconstruct annual flows (for example, the research summarized in the National Institutes/PubMed source) show a sharp drop in annual arrivals after 2001 and emphasize departures (emigration, adjustments, removals, deaths) as important in net population change, but those publications in the supplied snippets report trajectories and peaks rather than an explicit 2001–2008 aggregate usable without accessing their tables directly [1].
5. Alternative viewpoints and methodological caveats
Some demographic models (noted in broader literature excerpts) yield substantially larger totals when different assumptions about census undercount or demographic processes are used — for example, alternative models have produced much higher nationwide estimates for undocumented populations — illustrating that method choice matters and that any derived 2001–2008 figure would be model-dependent [4] [5]. The DHS/OIS residual-method series and reconstructions cited here are the conventional baseline used by analysts and nonprofits like the American Immigration Council [2] [3].
6. Bottom line for the question asked
The best publicly cited benchmark from the supplied sources is that about 3.9 million undocumented immigrants arrived in the United States during the 2000s decade (2000–2009) [2]; the available reporting does not provide a direct, published sum limited to 2001–2008, but given the peak in 2000–2001 and the rapid decline thereafter [1], a reasonable interpretation is that the 2001–2008 subtotal would be somewhat less than 3.9 million — likely in the low-to-mid millions — while the exact count requires consulting the underlying DHS/OIS year-by-year tables or academic Table 3 referenced in the reconstruction study [1] [3].