Notes on Federal versus criminal law
The law says the following about entering this country illegally (really, it's a criminal violation):
(a) Improper time or place; avoidance of examination or inspection; misrepresentation and concealment of facts; Any alien who -
(1) enters or attempts to enter the United States at any time or place other than as designated by immigration officers, or
(2) eludes examination or inspection by immigration officers, or
(3) attempts to enter or obtains entry to the United States by a willfully false or misleading representation or the willful concealment of a material fact, shall, for the first commission of any such offense, be fined under Title 18 or imprisoned not more than six months, or both, and, for a subsequent commission of any such offense, be fined under Title 18, or imprisoned not more than two years or both."
Civil and federal crime
Being illegally in the U.S. is a civil matter. However, it is a federal crime to enter the country without inspection (EWI, USC 8 1325). A first offense can bring a fine and/or up to six months followed with deportation. A second offense (a felony) can bring up to two years and/or fine and then deportation. Thus, illegal immigration is a federal crime and a civil offense, with two separate courts.
The criminal charge will be filed by a U.S. Attorney and heard in U.S. District Court. The deportation (the removal) will then be conducted by the immigration courts, the Executive Office of Immigration Review (EOIR) before an Administration Law Judge.
Along the southern border, 95 percent of the cases get deposed of by "voluntary removal" on the part of the illegal, with no prosecutions in District Court. However, some U.S. Attorneys are indeed now filing all violations of USC 8, 1325. The U.S, Attorney in the Southern District of Texas is doing exactly that, with en masse proceedings. In Denver about one-half of detainees go through the formal deportation as outlined above.
Other commonly committed federal crimes include: the misdemeanor Failure to Carry Alien Registration. 18 USC 911, False Claim of US Citizenship, is a felony with an up to five-years in prison. Under 18 USC 1546, false document and fraud misuse on an I-9 claim is a felony.