Utah Const. art. XI, § 3

[Changing county lines.] (1) Except as provided in Subsection (2) , no territory may be stricken from any county unless a majority of the voters living in that county who vote on the proposition, as well as a majority of the voters living in the county to which it is to be annexed who vote on the proposition, shall vote therefor, and then only under such conditions as may be prescribed by general law. (2) Counties sharing a common boundary may, through their county legislative bodies, make a minor adjustment, as defined by statute, to the common boundary.