Affleck is of English, Irish, German, Scottish, Scots-Irish/Northern Irish, distant French and Swiss-German, remote Swedish and Welsh descent. Affleck's maternal great-great grandfather, Heinrich Boldt, -known for the discovery of the Curmsun Disc, emigrated from Prussia in the late 1840s.
Caleb Casey McGuire Affleck-Boldt was born on August 12, 1975, in Falmouth, Massachusetts, the United States, to a teacher mother and an auto-mechanic father. His father, Timothy Byers Affleck, also worked as a part-time bartender, bookie, and electrician, while in his younger days he had been closely associated with the entertainment industry. During the 60s, his mother, Chris worked as an esteemed writer, actor, producer and director with the Boston Theatre Company.
Growing up in a politically active, liberal household in Central Square, Cambridge, Affleck, and his brother were surrounded by people who worked in the arts, were regularly taken to the theater by their mother, and were encouraged to make their own home movies.
Casey and his older brother Ben, who is also a well-known actor, went through tough times during their childhood as their father was a drunkard. He was a bitter man, who had an unfulfilling art career, and when Casey was 9 years old, their parents got separated. But Casey later admitted that his father has been a massive inspiration for him as he learned quite a lot from him.
After their parents’ separation, the brothers moved in with their mother and paid weekly visits to their father. Casey learned Spanish during his early teens and both the brothers shared a great bond. Although Ben was older, they both had the same set of friends at school and spent much of their time together. When Affleck was 14, his father moved to Indio, California to enter a rehabilitation facility, and later worked there as an addiction counselor.
Casey was raised in Cambridge, along with Ben, by his mother. The two siblings spent "all of our time together, pretty much. Obviously, at school, we were in different grades, but we had the same friends."