Vincent was born in Denver, Colorado. His father, Lloyd Whiteley Vincent (September 7, 1919–August 30, 2000), was born in Tulare, California and raised in nearby San Joaquin Valley. His mother, Doris Jane (née Pace; August 2, 1925–February 22, 1993), was born in Arkansas and moved to Hanford, California as a toddler. Herbert Vincent (September 26, 1876–January 14, 1974), Jan's grandfather, was a bank robber and counterfeiter where he had masterminded robberies in the 1920s and 1930s. Lloyd's brother, Hoy, was shot to death in Tulare by a sheriff's deputy and was wanted for a robbery that happened in Oregon. Two of Vincent's uncles, Clifford and Harold, were convicted of bank robbery in Hardwick and Strathmore in 1931. In 1932, Herbert and his son, Gordon, were arrested in Hanford in January 1932 for bank robbery and assault with a deadly weapon, which left Lloyd with no one at the age of twelve. The couple met in 1940 when Doris was in her early teens, and Lloyd had finished high school. Lloyd was stationed in Denver in 1941 and a B-25 bomber pilot during World War II. His mistrust of authority came from seeing his father in the army being told what to do and when to do it. Doris and Lloyd married when she was sixteen and in Denver. Vincent's sister, Jaqueline "Jacquie", was born in 1947. His brother, Christopher, was born in 1952. After the war, his father became a painter like Vincent's grandfather and also became an alcoholic.