How does the US government track down illegal immigrants?

I'm not talking about raiding a workplace, where the employer is required to keep paperwork on each employee. I'm talking about arresting and deporting individuals, sometimes from their homes. In the US, people aren't required to carry paperwork or ID to prove their legal status. So how do they find illegal immigrants, other than workplace raids?

Knowledgeable answers only, please. I'm not interested in your off the cuff speculaton; I can do that for myself.
they dont...its all lip service

there is no way to determine if anyone is legal or not if they have paperwork..fake stuff takes a long time to verify..

we are fighting a losing battle in this country

we need to have martial law imposed as it relates to illegals

let the military hunt them down, and if the illegals try to run...deadly force is appropriate
Very poorly. If someone reports them, fine. Otherwise, little oversight and luck, mostly. That's why there are so many undocumented people here -- we simply don't track them.


Answer:
If not at work than usually a tip, or a traffic stop or some other choke point where ID is needed & the ID comes back stolen, forged, or the individual can't answer a basic question -- such as where & when he was born & his mother's maiden name. Often they have ID but have overstayed a visa, or they were paroled pending an asylum hearing & they don't show up for the hearing.
as an individual speaking from experiance ( i was deported from the u.s. after living there 40 years as a legal resident ) i can give you some insight. the i.n.s. or i.c.e has access to all goverment agencys including law enforcement. once a warrant has been issued in an individuals name a simple traffic stop is all it takes. a great number of individuals are caught simply beacause someone notified immigration of there statutus