Illegal immigration, or unauthorized immigration, occurs when foreign nationals, known as aliens or non-citizens,University of Minnesota Human Rights Center. (2003) STUDY GUIDE: The Rights of Non-Citizens. violate US immigration laws by entering the United States unlawfully, or by lawfully entering but then remaining after the expiration of their visas, parole or temporary protected status.
Between 2007 and 2018, visa overstays accounted for a larger share of the growth in the undocumented immigrant population of the United States than illegal border crossings, which declined considerably from 2000 to 2018. In 2022, 37% of unauthorized immigrants were from Mexico, the smallest share on record. El Salvador, India, Guatemala and Honduras were the next four largest countries. As of 2016, approximately two-thirds of unauthorized adult immigrants had lived in the US for at least a decade. As of 2022, unauthorized immigrants made up 3.3% of the US population, though nearly one-third of those immigrants have temporary permission to be in the United States, such as those in Deferred Action for Childhood Arrivals. According to an August 2025 Pew Research Center report, the unauthorized immigrant population grew by 3.5 million between 2021 and 2023, reaching a record 14 million. July 2024 data for border crossings showed the lowest level of border crossing since September 2020.
Opponents of illegal immigration worry about crime, as well as possible social and economic burdens caused by migration. However, studies and FBI data have consistently found that undocumented immigrants are less likely to commit crimes than native-born citizens in the United States. In Texas, for example, undocumented immigrants are arrested for violent and drug crimes at less than half the rate of native-born U.S. citizens, and a quarter the rate of native-born citizens for property crimes. Opponents also insist immigrants enter the United States through a formal process and do not want to reward those bypassing the system.
Research shows that illegal immigration increases the size of the US economy, contributes to economic growth, enhances the welfare of natives, contributes more in tax revenue than they collect, reduces American firms' incentives to offshore jobs and import foreign-produced goods, and benefits consumers by reducing the prices of goods and services. Economists estimate that legalization of the illegal immigrant population would increase the immigrants' earnings and consumption considerably, and increase US gross domestic product. Most scientific studies have shown that undocumented immigrants commit less crime than natives and legal immigrants. Sanctuary cities—which adopt policies designed to avoid prosecuting people solely for being in the country illegally—have no statistically meaningful impact on crime. Research suggests that immigration enforcement has no impact on crime rates.
Definitions The categories of foreign-born people in the United States are: US citizens born outside the United States who are naturalized or citizens by adoption. Non-citizens with current status to reside, work, or visit in the US (documented) Non-citizens without current status to reside, work, or visit in the US (undocumented) Non-citizens who are prohibited from entry (inadmissible)
The latter two fall under the category of illegal immigration. As they have no legal documentation to entitle them to be in the US, they are also referred to as undocumented immigrants or undocumented Americans. Persons who acquired US citizenship or nationality at birth, whether through birth on US territory, or through US citizen parents, are not classified as foreign born.
History
Rigorous immigration controls were first enacted with the Page Act of 1875, banning Chinese women, and the Chinese Exclusion Act of 1882, expanded to all Chinese immigrants.George Anthony Peffer, "Forbidden Families: Emigration Experiences of Chinese Women under the Page Law, 1875-1882" Journal of American Ethnic History (1986). 6#1: 28–46. online
Supreme Court decisions Since the late 19th century, various Supreme Court rulings established the Constitutional rights of noncitizens. In Yick Wo v. Hopkins (1886), the court ruled that under the Fourteenth Amendment, all residents, regardless of "race, of color, or of nationality" have the right to due process and equal protection under the law. A similar ruling of Wong Wing v. US (1896) stated that all persons within the territory of the United States are afforded equal protections under the Fifth Amendment and Sixth Amendment. A 1904 US Supreme Court decision concluded that deporting, "pursuant to law, an alien who has illegally entered the United States does not deprive him of his liberty without due process of law".Turner v. Williams, 194 U.S. 279 (1904) https://supreme.justia.com/cases/federal/us/194/279/
Legislation The Naturalization Act of 1906 required immigrants to learn English in order to become citizens. The Immigration Act of 1917 defined aliens with a long list of undesirables, including most Asians. The US had otherwise nearly open borders until the early 20th century, with only 1% rejected from 1890 to 1924, usually because they failed the mental or health exam.Alan M. Kraut, "Plagues and Prejudice: Nativism's Construction of Disease in Nineteenth- and Twentieth-Century New York City," in David Rosner, ed., Hives of Sickness: Public Health and Epidemics in New York City (New Brunswick, 1995), p. 70: "The number of immigrants returned to their ports of origin never excessed 3 percent of the new arrivals in any given year [during the 1890–1924 period of peak immigration], and the average for the entire period was well below 1 percent." While immigration laws during those years were loose, laws limiting naturalization to those of "white" and "African" descent meant many other immigrants had difficulty acquiring citizenship. These regulations immediately created problems of interpretation – the contentious question of who was and was not "white" vexed even the officials charged with enforcing the law and led to significant criticism. The Union of American Hebrew Congregations noted that under the standing interpretation that Turks, Syrians, Palestinians and Jews were not white, "even Jesus of Nazareth himself" would be excluded from citizenship. As a result, judges and immigration officials often admitted and naturalized technically ineligible people as a form of protest against the laws.
The Immigration Act of 1924 established visa requirements and enacted quotas for immigrants from specific countries, especially with low quotas for Southern and Eastern Europeans. Especially it affected Italians and Jews.Maddalena Marinari, Unwanted: Italian and Jewish mobilization against restrictive immigration laws, 1882–1965 (UNC Press Books, 2019) pp 43-70. It also prohibited all Asians from immigrating. By 1940, administrative and legislative action had loosened racial restrictions on naturalization of immigrants, including a ruling that Mexicans were considered white for immigration and naturalization purposes, and a law permitting the naturalization of "descendants of races indigenous to the Western Hemisphere." The quotas were eased in the Immigration and Nationality Act of 1952. The decisive opening came in 1965, a year after the Civil Rights Act of 1964 outlawed discrimination based on race or national origin. The Immigration and Nationality Act of 1965 abolished the quota system. The 1965 Act also established several new limits to which immigrants would be admissible for permanent residence in the United States.
The Immigration Act of 1990 increased the annual immigrant limit to 675,000 per year. In 1996, Congress debated two immigration bills, one focused on limiting legal immigration and another on illegal immigration. The legal immigration reform bills failed to pass, while the illegal immigration bill was passed in the form of the Illegal Immigration Reform and Immigrant Responsibility Act of 1996. President Bill Clinton signed the Act into law and it became effective on April 1, 1997. The key components of the Act included increasing the number of border agents, increasing penalties on those who smuggled immigrants into the United States, creating a 10-year re-entry ban on those who had been deported after living in the US illegally for over one year, and expanding the list of crimes that any immigrant (regardless of legal status) could be deported for.
In February 2024 and again in May 2024, Republicans in the Senate blocked a border security bill Joe Biden had pushed for to reduce the number of migrants who can claim the right of asylum at the border and provide more money for Customs and Border Protection officials, asylum officers, immigration judges and scanning technology at the border. It was negotiated in a bipartisan manner and initially looked like it had the votes to pass until Donald Trump opposed it, claiming that it would boost Biden's reelection chances. Five senators on the left voted against it for not providing enough relief for migrants already in the United States.
Border controls
As early as 1904, mounted border watchmen were employed by the US Immigration Service to prevent illegal southern border crossings. Texas Rangers were also often employed along the Texas border with Mexico.Joseph E. Chance, nd Milo Kearney, "The Legacy of the Texas Rangers on the Texas Mexico Border in Light of the Emergence of the Texas Minutemen." Further Studies in Rio Grande Valley History (2006): 171+. The US Border Patrol was also officially created in 1924, with its duties in 1925 broadened to include guarding the sea coast. Illegal entry into the United States became a particular problem during Prohibition, when bootleggers and smugglers would illegally enter the country to transport alcohol.
The debate over illegal immigration has continued amongst the fear of potential terrorist attacks in the wake of the September 11 attacks in 2001 and the lack of an effective Mexico–United States barrier. President Donald Trump enacted a travel ban from seven Muslim-majority countries, which was struck down as unconstitutional and replaced by a narrower version drafted by the Justice Department, which Trump described as "watered down, politically correct" and which was subsequently upheld by the Supreme Court. During his election campaign, Trump promised to make Mexico pay for a new border wall. The Mexican government refused to do so, and US taxpayers paid for the wall. The federal government entered a partial shutdown from December 22, 2018, to January 25, 2019, in a standoff over Trump's demand for $5.7 billion in funding for the wall.
US Marines scandal In 2020, 24 US Marines were discharged after an investigation over their alleged involvement in drug crimes and a human smuggling operation along the US–Mexico border. The investigation began when US Border Patrol agents arrested two marines for transporting three illegal Mexican immigrants on July 3, 2019. On July 25, 2019, 16 marines and a US Navy sailor were arrested on base during a battalion formation. The last arrest occurred on December 2, 2019, when a marine was caught transporting two illegal Chinese immigrants near the border.