What Supreme Court decisions have discussed the phrase 'illegal alien' or related immigration terminology?

1. Plyler v. Doe: the clearest Supreme Court statement treating “illegal aliens” as people

In Plyler v. Doe the Court struck down a Texas statute denying public school funding for children not “legally admitted” and explicitly recognized that “illegal aliens who are plaintiffs ... may claim the benefit of the Equal Protection Clause,” saying that whatever their immigration status “an alien is a ‘person’ in any ordinary sense of that term” ^[1], a holding emphasized in summaries of the case ^[2].

2. Historic immigration precedents where the Court used the statutory term “alien”

Longstanding Supreme Court immigration jurisprudence routinely uses “alien” as the statutory term, a practice reflected in earlier decisions such as Fong Yue Ting and Knauff referenced in legal overviews; those cases helped establish the civil-administrative character of exclusion and deportation adjudications and showed the Court’s reliance on the label “alien” in framing due process questions ^[6].

3. Recent invocations and the Alien Enemies Act litigation

Contemporary reporting shows the Court continuing to deploy “alien” formulations when adjudicating high‑stakes removal and national‑security questions: press coverage of a 2025 Supreme Court decision permitting the government to pursue certain removals under the Alien Enemies Act discusses the term “alien enemies” in majority and dissenting commentary, and notes that due process and judicial review remain contested in practice ^{[7] [8]}.

4. When justices first used “illegal alien” in formal opinions and contested usages

Analysts and advocacy pieces identify Mohawk Industries, Inc. v. Carpenter as an early instance of a Justice using the phrase in a formal opinion, and conservative advocacy groups cite later federal opinions that repeatedly use “illegal alien” as evidence the term is standard in judicial rhetoric ^{[5] [9]}. At the same time, commentators note that the phrase has no single statutory definition and that its prevalence in opinions is striking given that immigration statutes typically use “alien” without qualification ^[3].

5. Appellate and academic trends: judges substitute “noncitizen” or “undocumented”

Scholars tracking appellate opinions find deliberate terminological shifts in some circuits — for example, appellate judges sometimes replace quoted statutory “alien” with “[noncitizen]” to reflect a different framing, with empirical work showing such substitution in a measurable minority of opinions and sparking intra‑judicial disagreement about fidelity to statutory language ^[4].

6. The politics of language and competing narratives

Advocacy organizations and commentators argue in opposite directions: some insist “illegal alien” is precise legal terminology describing a status that violates immigration law (as argued in sources defending the term) while others emphasize the dehumanizing effects of “alien/illegal” and promote alternatives like “noncitizen” or “undocumented,” a debate visible in law reviews and policy briefs ^{[10] [9] [5] [4]}.

7. What reporting documents — and what it does not

Available reporting and scholarship establish that the Supreme Court and lower federal courts have repeatedly used “alien” and have sometimes used or been quoted as using “illegal alien,” and they document both historical examples (Plyler; earlier exclusion cases) and contemporary controversies (Alien Enemies Act litigation, appellate substitution trends) ^{[1] [6] [7] [4]}. These sources do not provide a definitive, exhaustive catalog of every Supreme Court opinion that has used the phrase; therefore a comprehensive list beyond the cited decisions cannot be asserted on the basis of the supplied materials ^{[3] [11]}.