Final answer:
The largest special jurisdiction police agency in the United States is the United States Department of Homeland Security (DHS). DHS operates at a federal level distinct from local county police, focusing on tasks like border security, counter-terrorism, and cybersecurity.
Step-by-step explanation:
Many metropolitan police departments are supplemented by special jurisdiction police agencies. The largest special jurisdiction agency in the United States is the United States Department of Homeland Security (DHS). Unlike local or county police departments, the DHS has a broader scope of responsibility, including securing the nation's borders, protecting against and responding to terrorist attacks, and ensuring safe and secure cyberspace. While local police departments focus on community-level law enforcement and emergency responses, federal officers from agencies like the DHS, the FBI, or the ATF are more involved in specialized tasks such as investigating cross-state criminal activities and providing security for critical infrastructure and government officials.