In the film The Departed, Billy Costigan lives in what city?

In The Departed, Leonardo DiCaprio stars as Billy Costigan, a promising police cadet at the Massachusetts State Police Academy. He is picked for a dangerous undercover job. But before he is given a chance to pin on an official policeman's badge, he is asked to work and live in the city of Boston, Massachusetts to fulfill a hazardous job as an undercover agent.

In The Departed, it is a gritty crime drama that is set in South Boston. Here the state police department is waging an all-out war on bad cops and organized crime members. Proper authorities want to end the control and power of mob boss Frank Costello (Jack Nicholson).

The lives of two cops: Colin Sullivan (Matt Damon) and Billy Costigan (Leonardo DiCaprio) are involved. Smart and unabashedly ambitious, Colin appears to be on a fast track, while working as an investigator in the police department's Elite Special Investigations Unit. Mob boss Costello is the prime target of this unit. In contrast to many cops, Billy Costigan is street-smart, clever and tough, but he suffers from a fierce temper. It is believed that his temper and harsh actions cost him his badge. He eventually lands back on the rough streets of South Boston, where he is recruited into Costello's crime organization.

Bluntly told, this is a story about people and public corruption. Is the infectiousness of crime hard for good individuals to detect and beat?