In 2021 how many undocumented or illegals were in the USA

1. The leading mainstream numbers and who published them

Pew Research Center’s estimate for 2021 is 10.5 million unauthorized immigrants, a figure produced using the residual method and American Community Survey (ACS) adjustments that Pew and many researchers use ^[1]. The Migration Policy Institute, working with updated imputations, put the mid‑2021 unauthorized population at about 11.2 million and MPI’s data products and summaries also show national estimates in the 11.2–11.4 million range ^{[2] [3]}. These estimates are the ones most often cited in academic and policy reporting for 2021 because they derive from large federal surveys adjusted to account for legal residents.

2. Other institutional and government perspectives

The Office of Homeland Security Statistics and other DHS products use similar residual‑type approaches and publish year‑by‑year tables and trends that inform analysts’ estimates; DHS methodology and time series are part of the standard evidence base even where explicit 2021 national totals differ across reports ^[6]. The Center for Migration Studies and Robert Warren have produced closely related series that show small differences in timing and totals but sit in the same general ballpark as MPI and Pew for that period ^[7].

3. Lower and higher outliers and why they differ

Some organizations have produced lower January‑2021 snapshots — for example the Center for Immigration Studies produced a CPS‑based estimate that cited about 10.22 million in January 2021 — while others and certain CPS treatments show slightly higher monthly counts near 11 million depending on timing and data source ^[8]. At the other extreme, a 2018 Yale demographic model estimated a much larger undocumented population (about 22.1 million), but that result has been criticized by other researchers for assumptions about circular flows and other parameters and is not the consensus estimate for 2021 ^{[4] [9]}.

4. Why estimates vary: methods, timing and population flows

Most mainstream estimates rely on a residual method subtracting counted legal foreign‑born residents from total foreign‑born population counts in the ACS or CPS; small differences in how undercounts are adjusted, which survey years are pooled, and whether estimates target mid‑year versus January snapshots produce multi‑hundred‑thousand differences in 2021 totals ^{[5] [1]}. Additionally, migration flows increased rapidly around 2021, so mid‑year versus end‑year measures and how researchers impute recent arrivals materially affect the numbers reported ^{[2] [7]}.

5. What a straightforward answer looks like

For 2021 the best short answer drawn from mainstream, peer‑reviewed and widely used residual estimates is: roughly 10.5–11.4 million people living in the United States without authorization, with Pew at 10.5 million and MPI/CMS‑linked estimates clustered around 11.2–11.4 million ^{[1] [2] [3]}. Acknowledging methodological uncertainty, most experts treat figures in that range as the most defensible baseline for 2021 rather than the much higher or much lower outliers ^{[5] [4]}.

6. Caveats and what reporting does not settle

These numbers are model‑based estimates, not headcounts; they depend on survey accuracy, assumptions about undercount rates and on how rapidly recent migration changed the population — issues explained in methodological reviews and Q&As from Pew, CMS, MPI and government analysts, which caution that year‑to‑year revisions can alter short‑term totals ^{[5] [10]}. Where a claim falls outside the mainstream range, the sources either explicitly defend unusual assumptions or face critiques in the literature; the public record does not definitively settle a single precise number for every month of 2021 ^{[4] [9]}.