The county legislative authority shall prescribe by resolution within what time such assessment or installments thereof shall be paid, and shall provide for the payment and collection of interest and the rate of interest to be charged on that portion of any assessment which remains unpaid over thirty days after such date. Assessments or installments thereof which are delinquent, shall bear, in addition to such interest, such penalty not less than five percent as shall be prescribed by resolution. Interest and penalty shall be included in and shall be a part of the assessment lien. All liens acquired by the county hereunder shall be foreclosed by the appropriate county officers in the same manner and subject to the same rights of redemption provided by law for the foreclosure of liens held by cities or towns against property in local improvement districts.