Utah Code § 17-61-407: Division of taxes.

(1) When a new county is created under the provisions of this part and the county officers of the new county have been elected:

(a) the county treasurer of the seceding county shall provide to the county treasurer of the new county a certified list of all taxes collected by the county treasurer of the seceding county for the preceding year upon the property located within the portion of the seceding county that has become a part of the new county; and

(b) subject to Subsection (2), the county treasurer of the seceding county shall provide to the county treasurer of the new county the county, school district, or other special tax revenue collected by the county treasurer of the seceding county for the preceding year within territory that has become part of the new county.

(2) Before furnishing the revenue described in Subsection (1)(b) to the new county, the seceding county may retain:

(a) the pro rata cost of assessing and collecting the county, school district, or other special tax revenue collected by the seceding county; and

(b) the entire cost of making the certified lists described in Subsection (1)(a).