Said county treasurer must append to and post with the delinquency list a notice that unless the assessment delinquent together with interest and costs are paid, the real property upon which said assessments are a lien will be sold at public auction. Said notice and delinquent list shall be posted at least twenty days prior to the date of the sale. One copy thereof shall be posted in the office of the county treasurer making the collection, one copy in the office of the board of directors, and one copy in each of three public places in the portion of said general improvement or divisional district lying in said county.