US population is showing a healthy growth and the share of immigrants among its population is only growing.
https://www.census.gov/popclock/
My question is, where are these immigrants coming from and what routes are they taking to get their US citizenship?
The United States does not have a restrictive immigration policy. Donald Trump wants it to have a more restrictive immigration policy. The US has the largest foreign born population in the world. Source.
Many of the countries with a higher foreign-born percentage are considerably smaller. Only the United Arab Emirates, Saudi Arabia, Australia, and Germany have more than five million foreign born citizens among countries with a higher percentage than the US. Many of the larger populations are in Europe, where they may reflect migration inside the European Union. That kind of migration exists in the US as well, but is not counted as immigration.
The US adds about seven hundred thousand people a year by naturalization. While 2017 was lower than 2016 and 2015, it was higher than 2014, 2011, and 2010.
The US adds roughly a million people a year legally, mostly as temporary residents. Some of these may naturalize later, but some return to their native countries.
The US has about eleven million people illegally in the US.
Immigrants have more children than US natives. Your source includes such children in its count. So the leading "immigration" method is to be born in the US. Most sources would not consider them immigrants, but apparently your source does.
The next leading method is family reunification. This includes spouses as well as relatives (often of the spouses). So if someone naturalizes, that person can then sponsor parents, siblings, children, etc. This is about half of legal immigration.
Some other sources:
Mexico is the top origin country of the U.S. immigrant population. In 2016, 11.6 million immigrants living in the U.S. were from there, accounting for 26% of all U.S. immigrants. The next largest origin groups were those from China (6%), India (6%), the Philippines (4%) and El Salvador (3%).
By region of birth, immigrants from South and East Asia combined accounted for 27% of all immigrants, a share equal to that of Mexico. Other regions make up smaller shares: Europe/Canada (13%), the Caribbean (10%), Central America (8%), South America (7%), the Middle East (4%) and sub-Saharan Africa (4%).
From Pew Research (September 14, 2018) citing the 2016 American Community Survey (a product of the U.S. Census Bureau).
The means by which immigrants secure lawful permanent residency (which is a prerequisite to naturalization, as discussed below) varies considerably from country to country.
Family immigration is more common in places that have already sent many immigrants to the United States. Refugee immigration is more common in places that are war torn or repressive. In much of Asia, work related immigration makes up a disproportionate share of all legal immigration to the United States. Lottery based immigration makes up a disproportionate share of immigration from countries without much of a history of immigration to the United States, especially in the Third World.
Routes To Citizenship
Citizenship For Foreign Born Non-Citizens
All foreign born persons seeking to get their U.S. citizenship (subject to an exception of a dozens of people currently living who have done so via private bills in Congress), do so by securing lawful permanent resident immigration status, and then applying to be naturalized and completing that process successfully.
The naturalization process involves a test, that basically covers English language proficiency and civics knowledge, and a background check (or being a minor child of a U.S. citizen who is naturalized who is included in a parent's application).
Spouses of U.S. citizens can apply for naturalization for themselves and their foreign born minor children three years after receiving lawful permanent resident status, other applicants must wait for five years after obtaining lawful permanent resident status (commonly called a "green card" even though the relevant document is no longer green).
It takes on the order of six months to a year (but sometimes longer) to have an application for naturalization approved, an one can apply 90 days before you are eligible to be naturalized based upon the number of years you have had a green card and the way you secured the green card (i.e. either 3 years or 5 years after getting a green card).
Non-Immigrant Paths To U.S. Citizenship
Anyone born in the United States, other than a child of foreign diplomats, is a U.S. citizen without regard to the citizenship or immigration status of their parents, as are the children of U.S. citizens regardless of where they are born (subject to confirmation of paternity within a certain time period when the U.S. citizen parent is a father rather than a mother).
This means that the U.S. born children of naturalized citizens, lawful permanent residents, people in the U.S. on temporary visas (even as tourists), and unauthorized immigrants are all U.S. citizens, even if they leave the U.S. shortly after they are born and have never returned to the U.S. (The U.S. rule on who can be a U.S. citizen is much less restrictive than in many other countries, which base citizenship solely on parental citizenship and naturalization without regard to place of birth.)
This also means that foreign born people with U.S. citizen parents are U.S. citizens, even if they have never set foot in the U.S., even if they are not raised at all by their U.S. citizen parent or parents, in the vast majority of circumstances (the exceptions to this general rule are highly technical and impact a quite small number of people), even though a not unreasonable definition of "immigrant" would include them if they came to the United States.
The "Indians not taxed" exception to birthright citizenship in the 14th Amendment's birthright citizenship clause is "spent." This category of persons was automatically granted citizenship by statute in 1924.
There is also what I call the "Superman" clause, in U.S. naturalization statutes, which provides that very young children of unknown paternity found in the U.S. are U.S. citizens (unless their citizenship is affirmatively disproved in a citizenship adjudication revealing their paternity and place of birth before they reach adulthood). This exception affects a very small number of people each year.
Citizenship can also be awarded by statute to an individual by Congress via what is called a "private bill" which is a law enacted solely to benefit one or a few identifiable individuals.
Routes To A Green Card
The main bottleneck to securing U.S. citizenship for immigrants is obtaining lawful permanent resident immigration status. There are a variety of paths to a green card, most of which boil down to family ties, work related immigration and refugee based immigration.
1. Immediate Relatives of U.S. Citizens
There is no limit to the number of immediate relatives who can receive green cards each year and the number of people who receive green cards by this route are significant.
2. Preference Relatives of U.S. Citizens and Lawful Permanent Residents
A limited number (480,000) of green cards are given out to other relatives of U.S. citizens and lawful permanent residents. The wait tends to range from three to twenty four years. Brothers and sisters of U.S. citizens wait the longest.
The wait is longer for family members from some countries than it is from others in this category. People from Mexico and the Philippines, for example, face very long wait times in this categories of preferred family members.
The following are the preferences in order of preference:
3. Employees and Workers
A total of 140,000 green cards are available each year for people whose job skills are needed in the U.S. market and who offer skills which an employer cannot find from the local market of U.S. workers.
In most cases, a job offer is required before the immigrant can seek a green card, and the employer needs to begin, and actively participate in the application process.
In three categories, however, a job offer is not required. These include investors (fifth preference, described below); workers of "extraordinary ability" (a subcategory of the first preference priority workers category described below); and workers with "exceptional ability," a subcategory of the second preference category.
Complex rules govern priorities within employment based categories.
4. Special Immigrants
This category contains an odd mix of visa types, many of them too narrow to be useful to more than a few people. Special immigrants include:
Religious workers (clergy as well as other people in a "religious vocation," such as religious instructors, cantors, and workers in religious hospitals).
Foreign medical graduates who came to the U.S. before January 10, 1978 on an H or J visa and meet various other conditions.
Former international U.S. government workers.
Retired employees of international organizations.
Persons declared dependent on a juvenile court.
Service people with 12 years' duty.
5. Refuge and Political Asylum
The U.S. government offers refuge to people who have a fear of, or have experienced, persecution in their home country based on race, religion, nationality, political opinion, or membership in a particular social group. The U.S. government sets a different limit on refugee admissions -- those who come from overseas -- each year. In 2018, the cap was 45,000 and the Trump administration proposes to reduce that cap in 2019 to 30,000. There is no limit on the number of people who can, from within the U.S., apply for asylum each year.
Refugees and people granted asylum can apply for a green card one year after receiving their status.
6. Long-Time Residents - Cancellation of Removal
In some instances, people who have lived in the United States continuously for more than ten years, have good moral character, can show that their spouse or children are U.S. citizens and would face "extraordinary and exceptionally unusual hardship" if the alien were forced to leave the U.S., and have been placed in removal proceedings, can request permanent residence from the judge.
Note that while there is substantial text overlap between the material above and the source material linked, this is mostly because the source material is a very close paraphrase of the underlying statutes, regulations and government publications.
This question seems to be posed by the title to this question even though it doesn't appear in the question's body text.
There are two ways (technically there is also a third) that the U.S. Population can grow or shrink.
One is called "natural increase" which means that births in the U.S. exceed deaths in the U.S. As of 2015, the annual rate of natural increase in the U.S. population was 0.423%. (At its peak in 1966, the annual rate of natural increase in the U.S. population was 0.9%).
The second is net immigration. This is the number of people who migrated to the U.S. minus the number of people migrate from the U.S. in any given year. As of 2015, the net immigration rate for the U.S. population was 0.286%. (The foreign born population increased 1% from 2015 to 2016, but about 71% of this net immigration of foreign born persons was offset by migration out of the U.S. by person who were not foreign born.)
So, net immigration is the source of about one-third of U.S. population's combined annual growth rate of 0.709% (which is equivalent to 7.3% per decade).
Both total U.S. population growth and natural increase in the United States are higher than in most of its peer developed countries.
Finally, the U.S. population can increase when it adds territory with people in it (as it did, for example, following the Spanish-American War in 1896 that added Puerto Rico and the Philippines to the United States), and can decrease when it grants independence to U.S. territory with people in its (as it did, for example, when the Philippines and Palau respectively were granted independence from the United States). Obviously, this happens only infrequently and sporadically and has not happened for many years in the U.S.
Note that the term "population" refers to people who reside in a country, and not only to people who are citizens of a country. In round numbers about 14% of the U.S. population is foreign born and U.S. citizens make up about 93% of the U.S. population.
In 2016, about 49 percent of immigrants (21.2 million) were naturalized citizens. The remaining 22.5 million included lawful permanent residents, unauthorized immigrants, and legal residents on temporary visas (such as students and temporary workers).
About two-thirds of foreign born persons in the United States with legal immigration status are naturalized citizens (naturalized citizens make up about 7% of the U.S. population). Legal immigrants who are not naturalized citizens make up about 3.5% of the U.S. population.
Also, since many foreign born persons who are legally in the United States (e.g. exchange students) are not eligible to be naturalized because they have temporary visas rather than lawful permanent resident status or haven't been lawful permanent residents for enough years, significantly more than two-thirds of legal immigrants in the United States who are eligible to become naturalized citizens do so. Some people who are lawful permanent residents of the United States are are eligible to become naturalized citizens of the United States don't do so right away, or ever, but that is a decided minority of people eligible to do so.
One important subset of lawful permanent residents who do not seek to become naturalized citizens are people who immigrated to the U.S. in middle age or older (often to be with U.S. citizen children or as refugees) who believe (often accurately) that they are unable to do so because they have never managed to become fluent enough in the English language to have a good chance of passing the naturalization test. Learning a first foreign language fluently is much easier, as a matter of developmental neurology, if you are a young adult or a child, than it is if you are older than that age when you start learning the language.
A bit less than half of the foreign born persons in the U.S. who are unauthorized immigrants (a.k.a. undocumented immigrants a.k.a. illegal immigrants), this is about 11 million people (calculating the number is not an exact science), which constitutes about 3.5% of the U.S. population. There was no net change in the number of unauthorized immigrants in the United States from 2009 to 2014 (the most recent reliable data that I could locate) when the Great Recession and Financial Crisis stalled unauthorized immigration to the U.S., so 100% of the growth in the foreign born population of the United States for the most recent year available is due to legal immigration. About 52% of unauthorized immigrants in the United States are from Mexico. Latin American and Asia make up most of the balance of unauthorized immigrants in the United States.
As of 2016, there are about 9 million people who are U.S. citizens but are not part of the U.S. population because they live abroad, according to the State Department, who are called "expatriates". So roughly 97% of U.S. citizens live in the United States, and 3% of U.S. citizens are expatriates. The stack exchange platform has a forum devoted to them.
About 50.4% of the U.S. population is 35 years of age or older and about 42% of the U.S. population is eligible to be elected President by being natural born citizens age 35 years of age or older who have lived in the United States for at least fourteen years. (I don't formally account for people who were natural born U.S. citizens and lost that citizenship at some point in life and then moved back to the United States and became U.S. citizens again, but that number is vanishingly small, although probably not quite zero.)
There is some small amount of uncertainty due to uncertain legal definitions, as well as measurement error, in this percentage.
This is because while it is clear that someone born in the United States is a natural born citizen, and it is fairly widely accepted that someone who was a U.S. citizen at birth because their parents were U.S. citizens entitled to pass on their citizenship to their children at birth are natural born citizens, there are other gray areas.
It is not entirely clear what the legal status of someone who was made a citizen as of their birth by retroactive naturalization laws or retroactive judicial interpretations of naturalization laws (there have been several of both types of changes).
For example, it is not clear if someone who was an "Indian not taxed" when they were born in 1923 on a tribal reservation became a "natural born citizen" when the law was retroactively changed to make that person a citizen in 1924. A similar issue applies to certain people who were born outside the U.S. to a foreign mother and a U.S. father, who retroactively became U.S. citizens as a remedy based upon a judicial determination that U.S. citizenship law improperly discriminated based upon gender in imposing requirements on such children to be recognized as U.S. citizens.
Similarly, it is not entirely clear whether someone who was a natural born citizen of the place that they were born, which becomes territory of the United States after they are born, is a natural born citizen of the United States.
For example, is someone who was an Canadian citizen when born to Canadian parents in 1924 in the two and a half acres of the Lake of the Woods area that was transferred from Canada to the U.S. by treaty in 1925 a "natural born citizen", or what about someone born in the Northern Mariana Islands to local parents before it became a part of the United States in 1978?
Similarly, complications can arise when the place where you were born is in territory that ceases to be part of the United States.
For example, one U.S. Presidential candidate (Republican Senator John McCain) was born in the Panama Canal Zone which was U.S. territory from 1903 to 1978, but it is now part of the country of Panama. In that case, the fact that the candidate had U.S. citizen parents made the question of citizenship at birth based upon place of birth largely irrelevant, but if that candidate had foreign born parents, that candidate's status as a natural born citizen would have been less clear.
None of these questions has been officially resolved and each require constitutional interpretation on questions of first impression, which almost never arise to create precedents, because only a few people have been elected as, or served as President of the United States.
