Mich. Const. art. VI, § 15

In each county organized for judicial purposes there shall be a probate court. The legislature may create or alter probate court districts of more than one county if approved in each affected county by a majority of the electors voting on the question. The legislature may provide for the combination of the office of probate judge with any judicial office of limited jurisdiction within a county with supplemental salary as provided by law. The jurisdiction, powers and duties of the probate court and of the judges thereof shall be provided by law. They shall have original jurisdiction in all cases of juvenile delinquents and dependents, except as otherwise provided by law.