Maryland Code, Family Law § 5-204

(a)(1) If a minor child has only 1 parent, the domicile of the child is the same as that of the parent.

(2) If the parents of a minor child live together, and the child lives with them, the domicile of the child is the same as that of the parents.

(1) the parent to whom custody is awarded; or

(2) if custody has not been awarded, the parent with whom the child lives.