It has been abolished and its functions have been merged into the new Department of Homeland Security (what a name! When I grew up in Germany, the word Homeland was associated with a certain politician who was less than pleasant...) INS used to be part of Department of Justice. There are now three separate agencies that took over these tasks.

The first one is USCIS, or Bureau of Citizenship and Immigration Services. They administer all your applications.

The second one is BCBP, or Bureau of Customs and Border Patrol. As the name suggests, it actually derived from the old Customs agency and the old Border Patrol portion of INS. They handle the control of who and what comes across our borders.

The third one is BICE, or Bureau of Immigration and Customs Enforcement. The name suggests that this, too, originated from a merger of some INS and some Customs functions. Purpose of this agency is internal enforcement. They handle deportation hearings, for instance.