Immediately at the end of any term of court at which any decree for sales of real estate for the payment of taxes is rendered, or as soon thereafter as practicable, the tax collector shall proceed to enforce such decree by sales of real estate ordered to be sold, and to this end shall give notice for 30 days before the day of sale, by publication for three successive weeks in some newspaper published in the county, or at least three weeks before the day of sale shall post a notice at the courthouse of his county and at some public place in the precinct in which the real estate is situated that at the time specified therein he will proceed to sell such real estate separately, describing such portions as are embraced in each decree and stating the amount for which each decree was rendered (without stating the items of which said decree is composed) and the person against whom the taxes embraced in such decree were assessed or, if assessed to “owner unknown,” stating that fact.