The question of the difference between domicile and residency is subject to good debate in law schools. It is present in Rahm Emanuel’s court case involving his qualification to run for the elective office of Mayor of Chicago, Illinois.
Domicile is more of a “mental” concept, while residency requires physical presence. Emanuel argues more domicile concepts (that he always intended to return to Illinois). But the key to the case is where he resided (actual physical presence) last year.
Emanuel is appealing the decision.