In counties with 3,000,000 or more inhabitants, all payments of interest or costs under Sections 21-315 and 21-320 and subsection (c) of Section 21-310 shall be paid as provided in Sections 21-330, 21-335 and 21-340. In all other counties, the county treasurer may determine in his or her discretion whether payment of interest and costs shall be made as provided in Sections 21-330, 21-335 and 21-340. In the other counties, where the treasurer determines not to make payment as provided in those subsections, the treasurer shall pay any interest or costs under this Section pro rata from those accounts where the principal refund of the tax sale purchase price under Section 21-310 is taken.
35 ILCS 200/21-325