If the borough of Brooklyn were a city on its own, it would be the fourth largest in the United States by population. More than 2.5 million people currently call Brooklyn home. Whether you love it or hate it, people usually have strong feelings about Brooklyn and the people who live there. Back in the 19th century Brooklyn was a city, distinct and separate from New York City, with its own government and services, including a police department. This is the story of the Brooklyn Police department.