Your County Treasurer bills property taxes from the Tax Roll Warrant certified by the County Assessor. Collected taxes are then apportioned and distributed by the Treasurer to the various taxing authorities (authorities in your district are listed on your statement). You can see an estimated use of your taxes by checking the Property Tax Distribution Calculator.
Mill Levies/Tax Rates are set by the taxing authorities (County Commissioners, School Boards, Town Council and directors of districts). Taxes are calculated by multiplying the Assessor's assessed value times the tax rate. The Treasurer does not determine either the tax rate or the assessed value.