The film's UK release, scheduled for 28 December 2007, was postponed for almost six months because of the film's similarity to the real-life case of four-year-old Madeleine McCann who disappeared from the holiday apartment where she and her family were staying in Praia da Luz, Portugal, on 3 May 2007.
Broadway actress Amy Ryan looked and sounded so convincing as a low class Dorchester mom that a security guard mistook her for a fan on the first day of location filming, and wouldn't let her on the set. One of the producers finally noticed her on the other side of one of the barricades, and said she should be let through. The incident made Ryan twenty minutes late, but convinced her the Boston accent she'd prepared was realistic.
Amy Ryan was so convincing with her Boston accent in her audition, that director Ben Affleck asked her what part of Boston she was from
According to the DVD commentary, the flyover shot of the quarry is a special effects shot, since the quarry actually had no water.
Jill Quigg was discovered when the production's barricades in the streets of Boston prevented her from picking up her son from school. Ben Affleck was so impressed by her loud rants against the film crew that he asked her to read for the movie.
Ben Affleck initially considered starring in the film.
Ben Affleck's high school chemistry teacher (Ed McGillicuddy) makes a cameo appearance in the scene when they are leaving the funeral.
The character of Jerome Miller (a.k.a. "Bubba", Patrick's drug-lord friend) is played by Boston hip-hop performer Slaine. In the scene where Bubba and Patrick are driving up to Everett to meet Leon and Roberta Trett, the song playing on the stereo in their SUV is by Slaine.