In the US you find both. More commonly CS came from electrical engineering, but you do find some departments that started as part of mathematics. In any case,

In the US you find both. More commonly CS came from electrical engineering, but you do find some departments that started as part of mathematics. In any case, as other commenters said, early "computer scientists" often came from physics, math, electrical engineering, etc. (Abelson & Sussman themselves had PhDs in mathematics.)