The United States of America is the primary destination for more members of the global migrant population than any other country. Between those in the country with non-immigrant visas, Permanent resident visas, work visas, refugee or asylum status, or with no authorization at all, nearly 47 million in 2015, according to statistics kept by the United Nations.
To handle the constant influx of foreign individuals - both legally-authorized and otherwise - across the borders, the federal government relies on a handful of agencies to funnel foreign visitors and residents in and out of the country. They, in turn, rely on state and local governments and law enforcement to aid them. The whole process requires a lot of manpower, money, paperwork, and waiting, and it’s been a battleground of high emotion even before the most recent moral crises surrounding Arizona’s SB 1070 of 2010, the extreme uptick in South American migration in 2014, and President Trump’s insistence upon prohibiting the travel of those from particular Middle Eastern countries.
The Freedom of Information Act and equivalent state laws can help to shed some light into how the immigration system on all levels is working - or not. Even for those tangled in the system itself, with pending immigrant applications, filing a FOIA can be the only way to get a sense for what information the government is holding onto regarding the applicant. And for those curious about which and how private companies are benefiting from the chaos of the federal immigration system, it can be the best way to get a solid look at the costs associated with immigrant detention.
MuckRock has a growing collection of requests that can be used for research or as a reference point for future inquiries.
The Department of Homeland Security - which houses three of the primary agencies associated with immigration: U.S. Citizenship and Immigration Services, Customs and Border Protection, Immigration and Customs Enforcement, - publishes an annual Immigration Statistics Yearbook, though upon request further or more detailed visa and deportation statistics is likely available. Additionally, one may be able to obtain operation plans or reports related to the mission of immigration enforcement.
The technology being purchased by these agencies is also typically subject to disclosure, though concerns around security could warrant certain redactions …
and not all materials related to private management, such as the privately-operated immigrant detention centers that hold over two-thirds on those detained on immigration charges, will be made readily available.
For historical records, related to Immigration and Naturalization Services, the predecessor to the current immigration agencies, consult the National Archives and Records Administration.
On the more local level, ICE and the U.S. Marshals Service frequently enter into partnerships with local law enforcement to help them identify and expand their ability to apprehend those with immigration violations. Additionally, local communications related to policies of immigration enforcement.
Other organizations have more to offer regarding learning about the immigration system in the U.S. In particular, Transactional Records Access Clearinghouse collects regular reports on detention, immigrant detainers, courts, and deportations.