The St. Louis County Assessor's Office is responsible for administering the assessment for the County. This includes supervising and advising the local jurisdictions on assessment matters, conducting statistical studies of assessment ratios, preparing appraisals for the County Board of Equalization and Tax Court, and advising the County Board.

In addition, the County Assessor provides assessment services for all unorganized townships and the organized jurisdictions that contract with the County. This includes reappraisals of all parcels at least once every four years, inspection of changes which may affect value, administration of Homestead and other classifications, reviewing complaints from taxpayers, and assisting the local Boards of Review in evaluating appraisals.