Notice that the mortgage held by the authority will be foreclosed by a sale of the mortgaged premises, or some part of them, shall be given by publishing the same for 4 successive weeks at least once in each week, in a newspaper published in the county where the premises included in the mortgage and intended to be sold, or some part of them, are situated. If no newspaper is published in the county, the notice shall be published in a newspaper published in an adjacent county. In every case within 15 days after the first publication of the notice, a true copy shall be posted in a conspicuous place upon any part of the premises described in the notice.